What is the proof that David Archuleta is a Mormon?

Yes, David Archuleta is an active member of the Church of Jesus Christ of Latter-day Saints, which is often referred to as the "Mormon" church. You can find out more about his religious beliefs by visiting www.mormon.org.
Yes. David Archuleta is a member of the Church of Jesus Christ of Latter-day Saints (commonly called the "Mormon" church). You can see a video of him performing at a Mormon worship service at the "Related Links" below.