Trimble, who won the Nobel Peace Prize with then-Social Democratic and Labor Party Leader John Hume for his work on the 1998 Good Friday Agreement, was defeated in Upper Bann by David Simpson of the Democratic Unionist Party.
Speaking at a Belfast press conference, he blamed the government and republicans for not fully implementing the Good Friday agreement.
He also warned new Northern Ireland Secretary Peter Hain he would not make progress in the peace process if he continues the current policy path.
"He might also like to ask himself what other unionist leader is going to make an effort to implement the agreement when they see what has happened to the one leader who did unambiguously endeavor to do so," Trimble said.
Trimble said he believes the electorate voted for stalemate.