Fairley, 28, has had 14 career sacks since being chosen by the Detroit Lions in the first round of the 2011 draft.
Fairley joins a Saints defense that also includes former Rams middle linebacker James Laurinaitis, who was released in February.
Fairley played in 15 games last season as a back-up for Michael Brockers and Aaron Donald. He made 29 tackles, including a half-sack.
Fairley also reportedly drew interest this offseason from the New England Patriots and the Philadelphia Eagles.
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