diff --git a/alembic/versions/20260807_service_catalogue_registration_type_master.py b/alembic/versions/20260807_service_catalogue_registration_type_master.py
new file mode 100644
index 0000000..e8e867a
--- /dev/null
+++ b/alembic/versions/20260807_service_catalogue_registration_type_master.py
@@ -0,0 +1,45 @@
+"""Align Service Catalogue registration requirements with Registration Type master.
+
+The Service Catalogue previously used a frontend-only legacy code "GST" while the
+Registration Type master uses "GSTIN". Scope mapping compares these codes exactly.
+This migration updates only the legacy Service Catalogue value and leaves service
+IDs, service codes, firm selections, subscriptions, engagements, tasks and all
+other catalogue data unchanged.
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = "20260807_service_reg_master"
+down_revision = "20260806_related_person_scope"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    bind = op.get_bind()
+    inspector = sa.inspect(bind)
+
+    if "service_catalogues" not in inspector.get_table_names():
+        return
+
+    columns = {column["name"] for column in inspector.get_columns("service_catalogues")}
+    if "required_registration_type" not in columns:
+        return
+
+    bind.execute(
+        sa.text(
+            """
+            UPDATE service_catalogues
+               SET required_registration_type = 'GSTIN'
+             WHERE UPPER(TRIM(required_registration_type)) = 'GST'
+            """
+        )
+    )
+
+
+def downgrade():
+    # Deliberately do not restore GST. GSTIN is the canonical Registration Type
+    # master code and reverting it would reintroduce the scope-map mismatch.
+    pass
diff --git a/app/modules/services/templates/services/catalogue_form.html b/app/modules/services/templates/services/catalogue_form.html
index 1015ea9..a13312f 100644
--- a/app/modules/services/templates/services/catalogue_form.html
+++ b/app/modules/services/templates/services/catalogue_form.html
@@ -19,11 +19,18 @@
     <div id="registration-type-field"><label class="mb-2 block text-sm font-medium text-slate-700">Required Registration Type</label>
       <select name="required_registration_type" class="w-full rounded-xl border border-slate-300 px-4 py-2 text-sm">
         <option value="">Not applicable</option>
-        {% for value in ['GST','TAN','PF','ESI','PT','IEC','FSSAI','UDYAM','OTHER'] %}
-        <option value="{{ value }}" {% if catalogue and catalogue.required_registration_type == value %}selected{% endif %}>{{ value }}</option>
+        {% set current_registration_type = catalogue.required_registration_type if catalogue and catalogue.required_registration_type else '' %}
+        {% if current_registration_type and current_registration_type not in registration_type_codes %}
+        <option value="{{ current_registration_type }}" selected>{{ current_registration_type }} — Existing legacy value</option>
+        {% endif %}
+        {% for registration_type in registration_types %}
+        <option value="{{ registration_type.code }}" {% if current_registration_type == registration_type.code %}selected{% endif %}>{{ registration_type.code }} — {{ registration_type.name }}</option>
         {% endfor %}
       </select>
-      <p class="mt-1 text-xs text-slate-500">Used only for Registration-level services.</p>
+      <p class="mt-1 text-xs text-slate-500">Used only for Registration-level services. Values come from the active Registration Type Master.</p>
+      {% if request.query_params.get('error') == 'registration_type' %}
+      <p class="mt-1 text-xs font-medium text-red-600">Select an active Registration Type Master value.</p>
+      {% endif %}
     </div>
     <div><label class="mb-2 block text-sm font-medium text-slate-700">Sort Order</label><input type="number" name="sort_order" value="{{ catalogue.sort_order if catalogue else 100 }}" class="w-full rounded-xl border border-slate-300 px-4 py-2 text-sm"></div>
     <div class="flex items-center gap-6 pt-7 text-sm text-slate-700"><label class="inline-flex items-center gap-2"><input type="checkbox" name="is_active" {% if not catalogue or catalogue.is_active %}checked{% endif %}> Active</label><label class="inline-flex items-center gap-2"><input type="checkbox" name="is_client_requestable" {% if catalogue and catalogue.is_client_requestable %}checked{% endif %}> Client Requestable</label><label class="inline-flex items-center gap-2"><input type="checkbox" name="is_consultant_requestable" {% if catalogue and catalogue.is_consultant_requestable %}checked{% endif %}> Consultant Requestable</label></div>
diff --git a/app/modules/services/ui.py b/app/modules/services/ui.py
index f76b94a..a3267b4 100644
--- a/app/modules/services/ui.py
+++ b/app/modules/services/ui.py
@@ -14,6 +14,7 @@ from app.modules.core.audit.service import model_snapshot, pair_before_after, wr
 from app.modules.core.rbac.deps import get_user_permissions, get_user_roles
 from app.modules.core.rbac.permission_guard import require_permission
 from app.modules.core.tenancy.models import Branch
+from app.modules.registrations.models import RegistrationType
 from app.modules.services.models import FirmServiceSelection, FirmServiceTaskTemplate, ServiceCatalogue, ServiceCategory, ServiceDefaultTaskTemplate, ServiceDueDateRule, FirmTaskDocumentRequirement, FirmTaskDocumentTemplate
 from app.modules.services.bulk_imports import (
     build_template as build_bulk_import_template,
@@ -87,6 +88,50 @@ def _render(request: Request, template: str, db, user, **ctx):
     return templates.TemplateResponse(template, _base_ctx(request, user, db, **ctx))
 
 
+def _active_registration_types(db):
+    """Return the active Registration Type master rows used by Service Catalogue forms."""
+    return db.execute(
+        select(RegistrationType)
+        .where(RegistrationType.is_active.is_(True))
+        .order_by(RegistrationType.sort_order, RegistrationType.name, RegistrationType.code)
+    ).scalars().all()
+
+
+def _registration_type_form_context(db):
+    registration_types = _active_registration_types(db)
+    return {
+        "registration_types": registration_types,
+        "registration_type_codes": [row.code.upper() for row in registration_types],
+    }
+
+
+def _validated_registration_type_code(db, value: str, *, existing_value: str | None = None) -> str | None:
+    """Validate a submitted catalogue registration code against Registration Type master.
+
+    Existing non-master legacy values are allowed only when left unchanged so editing an
+    unrelated field never destroys historical catalogue data. New/changed values must be
+    active Registration Type master codes.
+    """
+    code = (value or "").strip().upper()
+    if not code:
+        return None
+
+    exists = db.execute(
+        select(RegistrationType.id).where(
+            RegistrationType.code == code,
+            RegistrationType.is_active.is_(True),
+        )
+    ).scalar_one_or_none()
+    if exists is not None:
+        return code
+
+    current = (existing_value or "").strip().upper()
+    if current and code == current:
+        return code
+
+    raise ValueError("registration_type")
+
+
 def _redirect_denied():
     from app.core.http_responses import ui_access_denied
     return ui_access_denied()
@@ -476,7 +521,7 @@ def catalogue_create_page(request: Request):
         if not _is_system_admin(db, user):
             return _redirect_denied()
         require_permission(db, user, 'services.create')
-        return _render(request, 'modules/services/templates/services/catalogue_form.html', db, user, title='Create Service Catalogue', mode='create', catalogue=None, categories=list_categories(db))
+        return _render(request, 'modules/services/templates/services/catalogue_form.html', db, user, title='Create Service Catalogue', mode='create', catalogue=None, categories=list_categories(db), **_registration_type_form_context(db))
     except Exception:
         return _redirect_denied()
     finally:
@@ -495,6 +540,10 @@ def catalogue_create_submit(request: Request, service_code: str = Form(...), ser
             return _redirect_denied()
         require_permission(db, user, 'services.create')
         selected_category = get_category(db, int(category_id)) if str(category_id).strip() else None
+        try:
+            registration_type_code = _validated_registration_type_code(db, required_registration_type)
+        except ValueError:
+            return RedirectResponse(url='/services/catalogue/new?error=registration_type', status_code=303)
         row = ServiceCatalogue(
             service_code=normalize_code(service_code),
             service_name=service_name.strip(),
@@ -503,7 +552,7 @@ def catalogue_create_submit(request: Request, service_code: str = Form(...), ser
             recurrence_type=recurrence_type.strip() or None,
             engagement_type=normalize_engagement_type(engagement_type),
             service_scope_type=(service_scope_type or 'client').strip().lower(),
-            required_registration_type=(required_registration_type or '').strip().upper() or None,
+            required_registration_type=registration_type_code,
             sort_order=sort_order,
             description=description.strip() or None,
             applicable_individual=applicable_individual is not None,
@@ -806,7 +855,7 @@ def catalogue_edit_page(request: Request, catalogue_id: int):
         row = get_catalogue(db, catalogue_id)
         if not row or not row.is_active:
             return RedirectResponse(url='/services/catalogue', status_code=303)
-        return _render(request, 'modules/services/templates/services/catalogue_form.html', db, user, title='Edit Service Catalogue', mode='edit', catalogue=row, categories=list_categories(db))
+        return _render(request, 'modules/services/templates/services/catalogue_form.html', db, user, title='Edit Service Catalogue', mode='edit', catalogue=row, categories=list_categories(db), **_registration_type_form_context(db))
     except Exception:
         return _redirect_denied()
     finally:
@@ -828,13 +877,22 @@ def catalogue_edit_submit(request: Request, catalogue_id: int, service_name: str
         if not row or not row.is_active:
             return RedirectResponse(url='/services/catalogue', status_code=303)
         selected_category = get_category(db, int(category_id)) if str(category_id).strip() else None
+        try:
+            registration_type_code = _validated_registration_type_code(
+                db, required_registration_type, existing_value=row.required_registration_type
+            )
+        except ValueError:
+            return RedirectResponse(
+                url=f'/services/catalogue/{catalogue_id}/edit?error=registration_type',
+                status_code=303,
+            )
         row.service_name = service_name.strip()
         row.category_id = selected_category.id if selected_category else None
         row.category = selected_category.name if selected_category else None
         row.recurrence_type = recurrence_type.strip() or None
         row.engagement_type = normalize_engagement_type(engagement_type)
         row.service_scope_type = (service_scope_type or 'client').strip().lower()
-        row.required_registration_type = (required_registration_type or '').strip().upper() or None
+        row.required_registration_type = registration_type_code
         row.sort_order = sort_order
         row.applicable_individual = applicable_individual is not None
         row.applicable_proprietorship = applicable_proprietorship is not None