Manager Derek McInnes moved for the 22-year-old, who was out of contract at Rugby Park.
Adams, who can play in midfield or defence, made just one substitute appearances in six years with Killie, with his career hampered by more than one serious knee injury.
He had various loan spells at Queen of the South and Partick Thistle and is hoping to kick-start his career at McDiarmid Park.
It proved a busy day for Saints, with midfielder Murray Davidson signing a one-year contract extension.
The highly-rated 22-year-old is now tied to the club until 2013.
Source: Team Talk
Source: Team Talk