Archuleta, 20, made the tearful announcement at a concert in his hometown of Salt Lake City on Monday to cheers and applause from the audience.
"I have chosen to serve a full-time mission for Jesus Christ and his Latter Day Saints," Archuleta told the audience. The singer also posted a video of his announcement on his official website.
"It's not because someone told me I was supposed to do it, not because I no longer want to do music anymore, but it's (what) I feel I need to do next in my life," the singer said.
Archuleta's decision will mean putting his music career on hold. Mormon missionaries are expected to put school, work and dating aside for two years to devote themselves to preaching the church's gospel.
Missionaries are also told not to watch television, use the Internet or take part in dangerous sports, and to go to bed at 10:30 pm each night.
Archuleta started singing at age six and began performing in public at age 10. In 2008, the baby-faced piano player became one of the youngest-ever finalists on "American Idol", finishing the TV singing contest as runner-up to David Cook.
His first album "Crush" debuted at No. 2 on the Billboard album chart and since then, he has a strong following of fans in the Philippines, Indonesia and Malaysia.