diff --git a/src/app/(observer)/observer/projects/[projectId]/page.tsx b/src/app/(observer)/observer/projects/[projectId]/page.tsx
index 8aa4689..c44148c 100644
--- a/src/app/(observer)/observer/projects/[projectId]/page.tsx
+++ b/src/app/(observer)/observer/projects/[projectId]/page.tsx
@@ -6,10 +6,13 @@ export const dynamic = 'force-dynamic'
 
 export default async function ObserverProjectDetailPage({
   params,
+  searchParams,
 }: {
   params: Promise<{ projectId: string }>
+  searchParams: Promise<{ round?: string }>
 }) {
   const { projectId } = await params
+  const sp = await searchParams
 
-  return <ObserverProjectDetail projectId={projectId} />
+  return <ObserverProjectDetail projectId={projectId} initialRoundId={sp.round} />
 }
diff --git a/src/components/observer/observer-project-detail.tsx b/src/components/observer/observer-project-detail.tsx
index bc611dc..d50e127 100644
--- a/src/components/observer/observer-project-detail.tsx
+++ b/src/components/observer/observer-project-detail.tsx
@@ -1,5 +1,6 @@
 'use client'
 
+import { useEffect, useState } from 'react'
 import Link from 'next/link'
 import type { Route } from 'next'
 import { useRouter } from 'next/navigation'
@@ -44,15 +45,41 @@ import {
 } from 'lucide-react'
 import { cn, formatDate, formatDateOnly } from '@/lib/utils'
 
-export function ObserverProjectDetail({ projectId }: { projectId: string }) {
+export function ObserverProjectDetail({
+  projectId,
+  initialRoundId,
+}: {
+  projectId: string
+  initialRoundId?: string
+}) {
   const router = useRouter()
+  const [activeRoundId, setActiveRoundId] = useState<string | undefined>(initialRoundId)
+
+  // Resolve a default round when none is set: prefer the currently OPEN round
+  // the project participates in, fall back to the most recently CLOSED one.
+  const { data: roundCandidates } = trpc.analytics.getProjectRoundsForObserver.useQuery(
+    { projectId },
+  )
+  useEffect(() => {
+    if (activeRoundId || !roundCandidates) return
+    const active = roundCandidates.find((r) => r.status === 'ROUND_ACTIVE')
+    if (active) {
+      setActiveRoundId(active.id)
+      return
+    }
+    const closed = [...roundCandidates]
+      .filter((r) => r.status === 'ROUND_CLOSED')
+      .sort((a, b) => b.sortOrder - a.sortOrder)[0]
+    if (closed) setActiveRoundId(closed.id)
+  }, [roundCandidates, activeRoundId])
+
   const { data, isLoading } = trpc.analytics.getProjectDetail.useQuery(
-    { id: projectId },
+    { id: projectId, roundId: activeRoundId },
     { refetchInterval: 30_000 },
   )
   const { data: flags } = trpc.settings.getFeatureFlags.useQuery()
 
-  const roundId = data?.assignments?.[0]?.roundId as string | undefined
+  const roundId = activeRoundId ?? (data?.assignments?.[0]?.roundId as string | undefined)
   const { data: activeForm } = trpc.evaluation.getStageForm.useQuery(
     { roundId: roundId ?? '', category: data?.project?.competitionCategory },
     { enabled: !!roundId },
@@ -223,6 +250,19 @@ export function ObserverProjectDetail({ projectId }: { projectId: string }) {
                     {stats.yesPercentage.toFixed(0)}% recommended
                   </p>
                 )}
+                {roundCandidates && roundCandidates.length > 1 && (
+                  <div className="mt-3 w-full">
+                    <select
+                      className="w-full rounded border bg-background px-2 py-1 text-xs"
+                      value={activeRoundId ?? ''}
+                      onChange={(e) => setActiveRoundId(e.target.value)}
+                    >
+                      {roundCandidates.map((r) => (
+                        <option key={r.id} value={r.id}>{r.name}</option>
+                      ))}
+                    </select>
+                  </div>
+                )}
               </div>
             </CardContent>
           </Card>
diff --git a/src/server/routers/analytics.ts b/src/server/routers/analytics.ts
index 7475433..7d52a17 100644
--- a/src/server/routers/analytics.ts
+++ b/src/server/routers/analytics.ts
@@ -2187,6 +2187,26 @@ export const analyticsRouter = router({
       }
     }),
 
+  /**
+   * Returns rounds the project has participated in, restricted to those that
+   * are open or already closed. Used by the observer full project page to
+   * resolve a default round when none is specified in the URL.
+   */
+  getProjectRoundsForObserver: observerProcedure
+    .input(z.object({ projectId: z.string() }))
+    .query(async ({ ctx, input }) => {
+      const states = await ctx.prisma.projectRoundState.findMany({
+        where: { projectId: input.projectId },
+        select: {
+          round: { select: { id: true, name: true, status: true, sortOrder: true } },
+        },
+      })
+      return states
+        .map((s) => s.round)
+        .filter((r) => r.status === 'ROUND_ACTIVE' || r.status === 'ROUND_CLOSED')
+        .sort((a, b) => a.sortOrder - b.sortOrder)
+    }),
+
   getRecentFiles: observerProcedure
     .input(z.object({ roundId: z.string(), limit: z.number().min(1).max(50).default(10) }))
     .query(async ({ ctx, input }) => {