diff --git a/backend/db/migrations/20260729144702-partial-unique-user-columns.js b/backend/db/migrations/20260729144702-partial-unique-user-columns.js
new file mode 100644
index 000000000..d180b6d5e
--- /dev/null
+++ b/backend/db/migrations/20260729144702-partial-unique-user-columns.js
@@ -0,0 +1,52 @@
+"use strict";
+
+// Columns that currently have a table-wide UNIQUE constraint but should only
+// be unique among non-deleted users, so a soft-deleted user's email/username
+// etc. can be reused by a new signup.
+const columns = ["email", "userName", "extId", "orcidId", "samlNameId"];
+
+function indexName(column) {
+  return `user_${column}_not_deleted_unique`;
+}
+
+module.exports = {
+  async up(queryInterface, Sequelize) {
+    await queryInterface.sequelize.transaction(async (transaction) => {
+      for (const column of columns) {
+        const [constraints] = await queryInterface.sequelize.query(
+          `SELECT con.conname
+           FROM pg_constraint con
+           JOIN pg_class rel ON rel.oid = con.conrelid
+           JOIN pg_attribute att ON att.attrelid = rel.oid AND att.attnum = ANY(con.conkey)
+           WHERE rel.relname = 'user' AND att.attname = :column AND con.contype = 'u'`,
+          {replacements: {column}, transaction}
+        );
+
+        for (const {conname} of constraints) {
+          await queryInterface.sequelize.query(`ALTER TABLE "user" DROP CONSTRAINT "${conname}"`, {transaction});
+        }
+
+        await queryInterface.addIndex("user", {
+          fields: [column],
+          unique: true,
+          where: {deleted: false},
+          name: indexName(column),
+          transaction,
+        });
+      }
+    });
+  },
+
+  async down(queryInterface, Sequelize) {
+    await queryInterface.sequelize.transaction(async (transaction) => {
+      for (const column of columns) {
+        await queryInterface.removeIndex("user", indexName(column), {transaction});
+        await queryInterface.addConstraint("user", {
+          fields: [column],
+          type: "unique",
+          transaction,
+        });
+      }
+    });
+  },
+};