diff --git a/app_test.go b/app_test.go
index 788df1e..df10e86 100644
--- a/app_test.go
+++ b/app_test.go
@@ -98,7 +98,7 @@ func TestParseCSVString(t *testing.T) {
 func TestGetCommands(t *testing.T) {
 	reg := NewCommandRegistry()
 	cmds := reg.GetCommands()
-	if len(cmds) != 14 {
+	if len(cmds) != 15 {
 		t.Errorf("expected 12 commands, got %d", len(cmds))
 	}
 	// Check that all have IDs
diff --git a/commands.go b/commands.go
index 467a54e..8c62e2a 100644
--- a/commands.go
+++ b/commands.go
@@ -32,5 +32,6 @@ func (c *CommandRegistry) GetCommands() []Command {
 		{ID: "open-right", Name: "Insert Column Right", Shortcut: ""},
 		{ID: "sort-asc", Name: "Sort A-Z", Shortcut: ""},
 		{ID: "sort-desc", Name: "Sort Z-A", Shortcut: ""},
+		{ID: "sort-advanced", Name: "Sort Advanced", Shortcut: ""},
 	}
 }
diff --git a/frontend/index.html b/frontend/index.html
index c4d8580..ad7ed40 100644
--- a/frontend/index.html
+++ b/frontend/index.html
@@ -25,6 +25,20 @@
             <input type="text" id="command-input" placeholder="Type a command..." />
             <div id="command-list"></div>
         </div>
+        <div id="sort-modal" class="hidden">
+            <div class="modal-title">Sort Advanced</div>
+            <div class="modal-body">
+                <label for="sort-columns-input">Columns (comma-separated, in priority order):</label>
+                <div id="sort-input-wrap">
+                    <input type="text" id="sort-columns-input" placeholder="e.g. Name, Age, City" autocomplete="off" />
+                    <div id="sort-autocomplete" class="hidden"></div>
+                </div>
+            </div>
+            <div class="modal-actions">
+                <button id="sort-cancel-btn" class="modal-btn">Cancel</button>
+                <button id="sort-confirm-btn" class="modal-btn modal-btn-primary">Sort</button>
+            </div>
+        </div>
         <div id="overlay" class="hidden"></div>
     </div>
     <script src="./src/main.js" type="module"></script>
diff --git a/frontend/src/main.js b/frontend/src/main.js
index e9a1e02..6213a51 100644
--- a/frontend/src/main.js
+++ b/frontend/src/main.js
@@ -26,6 +26,11 @@ const commandInput = $('#command-input');
 const commandList = $('#command-list');
 const overlay = $('#overlay');
 const tableContainer = $('#table-container');
+const sortModal = $('#sort-modal');
+const sortInput = $('#sort-columns-input');
+const sortAutocomplete = $('#sort-autocomplete');
+const sortConfirmBtn = $('#sort-confirm-btn');
+const sortCancelBtn = $('#sort-cancel-btn');
 
 // Default column width
 const DEFAULT_COL_WIDTH = 120;
@@ -609,6 +614,7 @@ async function loadCommands() {
             { ID: 'open-right', Name: 'Insert Column Right', Shortcut: '' },
             { ID: 'sort-asc', Name: 'Sort A-Z', Shortcut: '' },
             { ID: 'sort-desc', Name: 'Sort Z-A', Shortcut: '' },
+            { ID: 'sort-advanced', Name: 'Sort Advanced', Shortcut: '' },
         ];
     }
 }
@@ -691,7 +697,10 @@ commandInput.addEventListener('keydown', (e) => {
     e.stopPropagation();
 });
 
-overlay.addEventListener('click', closeCommandPalette);
+overlay.addEventListener('click', () => {
+    if (!commandPalette.classList.contains('hidden')) closeCommandPalette();
+    if (!sortModal.classList.contains('hidden')) closeSortAdvanced();
+});
 
 // ===== Command execution =====
 async function executeCommand(id) {
@@ -710,6 +719,7 @@ async function executeCommand(id) {
         case 'open-right': doInsertColRight(); break;
         case 'sort-asc': doSort(true); break;
         case 'sort-desc': doSort(false); break;
+        case 'sort-advanced': openSortAdvanced(); break;
     }
 }
 
@@ -936,6 +946,194 @@ function doSort(ascending) {
     setStatus(`Sorted by ${state.headers[col] || colLabel(col)} ${ascending ? 'A-Z' : 'Z-A'}`);
 }
 
+// ===== Sort Advanced Modal =====
+let acIndex = -1;
+
+function openSortAdvanced() {
+    sortModal.classList.remove('hidden');
+    overlay.classList.remove('hidden');
+    sortInput.value = '';
+    hideSortAutocomplete();
+    sortInput.focus();
+}
+
+function closeSortAdvanced() {
+    sortModal.classList.add('hidden');
+    overlay.classList.add('hidden');
+    sortInput.value = '';
+    hideSortAutocomplete();
+}
+
+function hideSortAutocomplete() {
+    sortAutocomplete.classList.add('hidden');
+    sortAutocomplete.innerHTML = '';
+    acIndex = -1;
+}
+
+function getCurrentToken() {
+    const val = sortInput.value;
+    const cursor = sortInput.selectionStart;
+    const before = val.substring(0, cursor);
+    const lastComma = before.lastIndexOf(',');
+    return {
+        text: before.substring(lastComma + 1).trim(),
+        start: lastComma + 1,
+        cursorPos: cursor,
+    };
+}
+
+function getAlreadyChosen() {
+    const parts = sortInput.value.split(',');
+    const cursor = sortInput.selectionStart;
+    const before = sortInput.value.substring(0, cursor);
+    const tokenIdx = before.split(',').length - 1;
+    return parts
+        .map(p => p.trim().toLowerCase())
+        .filter((_, i) => i !== tokenIdx)
+        .filter(p => p.length > 0);
+}
+
+function updateSortAutocomplete() {
+    const { text } = getCurrentToken();
+    const lower = text.toLowerCase();
+    const chosen = getAlreadyChosen();
+
+    const matches = state.headers
+        .filter(h => h.toLowerCase().includes(lower))
+        .filter(h => !chosen.includes(h.toLowerCase()))
+        .sort((a, b) => a.toLowerCase().localeCompare(b.toLowerCase()));
+
+    if (matches.length === 0 || (matches.length === 1 && matches[0].toLowerCase() === lower)) {
+        hideSortAutocomplete();
+        return;
+    }
+
+    sortAutocomplete.innerHTML = '';
+    sortAutocomplete.classList.remove('hidden');
+    acIndex = -1;
+
+    matches.forEach((name, i) => {
+        const div = document.createElement('div');
+        div.className = 'ac-item';
+        div.textContent = name;
+        div.addEventListener('mousedown', (e) => {
+            e.preventDefault(); // keep focus on input
+            applySortCompletion(name);
+        });
+        sortAutocomplete.appendChild(div);
+    });
+}
+
+function applySortCompletion(name) {
+    const val = sortInput.value;
+    const cursor = sortInput.selectionStart;
+    const before = val.substring(0, cursor);
+    const after = val.substring(cursor);
+    const lastComma = before.lastIndexOf(',');
+    const prefix = before.substring(0, lastComma + 1);
+    const spacing = lastComma >= 0 ? ' ' : '';
+    const newVal = prefix + spacing + name + after;
+    sortInput.value = newVal;
+    const newCursor = (prefix + spacing + name).length;
+    sortInput.setSelectionRange(newCursor, newCursor);
+    hideSortAutocomplete();
+    sortInput.focus();
+}
+
+function confirmSortAdvanced() {
+    const names = sortInput.value
+        .split(',')
+        .map(s => s.trim())
+        .filter(s => s.length > 0);
+
+    const colIndices = [];
+    for (const name of names) {
+        const idx = state.headers.findIndex(
+            h => h.toLowerCase() === name.toLowerCase()
+        );
+        if (idx === -1) {
+            setStatus(`Unknown column: "${name}"`);
+            return;
+        }
+        colIndices.push(idx);
+    }
+
+    if (colIndices.length === 0) {
+        setStatus('No columns specified');
+        return;
+    }
+
+    state.rows.sort((a, b) => {
+        for (const col of colIndices) {
+            const va = (a[col] || '').toLowerCase();
+            const vb = (b[col] || '').toLowerCase();
+            const cmp = va.localeCompare(vb, undefined, { numeric: true });
+            if (cmp !== 0) return cmp;
+        }
+        return 0;
+    });
+
+    closeSortAdvanced();
+    render();
+    setStatus('Sorted by ' + names.join(', '));
+}
+
+sortInput.addEventListener('input', updateSortAutocomplete);
+sortInput.addEventListener('focus', updateSortAutocomplete);
+sortInput.addEventListener('blur', () => {
+    // Small delay to allow mousedown on ac-item to fire
+    setTimeout(hideSortAutocomplete, 150);
+});
+
+sortInput.addEventListener('keydown', (e) => {
+    const items = sortAutocomplete.querySelectorAll('.ac-item');
+
+    if (e.key === 'Escape') {
+        e.preventDefault();
+        e.stopPropagation();
+        if (!sortAutocomplete.classList.contains('hidden')) {
+            hideSortAutocomplete();
+        } else {
+            closeSortAdvanced();
+        }
+        return;
+    }
+
+    if (e.key === 'Enter') {
+        e.preventDefault();
+        e.stopPropagation();
+        if (acIndex >= 0 && items[acIndex]) {
+            applySortCompletion(items[acIndex].textContent);
+        } else {
+            confirmSortAdvanced();
+        }
+        return;
+    }
+
+    if (e.key === 'ArrowDown' && items.length > 0) {
+        e.preventDefault();
+        if (acIndex >= 0) items[acIndex]?.classList.remove('active');
+        acIndex = (acIndex + 1) % items.length;
+        items[acIndex]?.classList.add('active');
+        items[acIndex]?.scrollIntoView({ block: 'nearest' });
+        return;
+    }
+
+    if (e.key === 'ArrowUp' && items.length > 0) {
+        e.preventDefault();
+        if (acIndex >= 0) items[acIndex]?.classList.remove('active');
+        acIndex = (acIndex - 1 + items.length) % items.length;
+        items[acIndex]?.classList.add('active');
+        items[acIndex]?.scrollIntoView({ block: 'nearest' });
+        return;
+    }
+
+    e.stopPropagation();
+});
+
+sortConfirmBtn.addEventListener('click', confirmSortAdvanced);
+sortCancelBtn.addEventListener('click', closeSortAdvanced);
+
 // ===== File loading =====
 async function loadFile(filePath) {
     try {
diff --git a/frontend/src/style.css b/frontend/src/style.css
index b858735..ea72bad 100644
--- a/frontend/src/style.css
+++ b/frontend/src/style.css
@@ -273,6 +273,124 @@ td.cursor-cell {
     border-radius: 3px;
 }
 
+/* Sort Advanced Modal */
+#sort-modal {
+    position: fixed;
+    top: 80px;
+    left: 50%;
+    transform: translateX(-50%);
+    width: 460px;
+    background: #fff;
+    border: 1px solid var(--border);
+    border-radius: 8px;
+    box-shadow: 0 8px 32px rgba(0,0,0,0.2);
+    z-index: 100;
+    overflow: visible;
+}
+
+#sort-modal.hidden {
+    display: none;
+}
+
+.modal-title {
+    padding: 12px 16px;
+    font-size: 15px;
+    font-weight: 600;
+    border-bottom: 1px solid var(--border);
+}
+
+.modal-body {
+    padding: 12px 16px;
+}
+
+.modal-body label {
+    display: block;
+    margin-bottom: 6px;
+    font-size: 13px;
+    color: #555;
+}
+
+#sort-input-wrap {
+    position: relative;
+}
+
+#sort-columns-input {
+    width: 100%;
+    padding: 8px 10px;
+    font-size: 14px;
+    font-family: inherit;
+    border: 1px solid var(--border);
+    border-radius: 4px;
+    outline: none;
+}
+
+#sort-columns-input:focus {
+    border-color: var(--selected-border);
+    box-shadow: 0 0 0 2px rgba(34,102,204,0.15);
+}
+
+#sort-autocomplete {
+    position: absolute;
+    left: 0;
+    right: 0;
+    top: 100%;
+    margin-top: 2px;
+    background: #fff;
+    border: 1px solid var(--border);
+    border-radius: 4px;
+    box-shadow: 0 4px 12px rgba(0,0,0,0.12);
+    max-height: 180px;
+    overflow-y: auto;
+    z-index: 110;
+}
+
+#sort-autocomplete.hidden {
+    display: none;
+}
+
+.ac-item {
+    padding: 6px 10px;
+    cursor: pointer;
+    font-size: 13px;
+}
+
+.ac-item:hover,
+.ac-item.active {
+    background: var(--selected-bg);
+}
+
+.modal-actions {
+    display: flex;
+    justify-content: flex-end;
+    gap: 8px;
+    padding: 10px 16px;
+    border-top: 1px solid var(--border);
+}
+
+.modal-btn {
+    padding: 6px 16px;
+    font-size: 13px;
+    font-family: inherit;
+    border: 1px solid var(--border);
+    border-radius: 4px;
+    background: #fff;
+    cursor: pointer;
+}
+
+.modal-btn:hover {
+    background: #f5f5f5;
+}
+
+.modal-btn-primary {
+    background: var(--selected-border);
+    color: #fff;
+    border-color: var(--selected-border);
+}
+
+.modal-btn-primary:hover {
+    background: #1a54a9;
+}
+
 /* Drag over style */
 #table-container.drag-over {
     background: var(--selected-bg);