The Russian will drive the BR Engineering BR01 car, after it spent a development year in the European Le Mans series.
SMP Racing are stepping up to a full WEC campaign in 2016, having competed in ELMS last season. The team finished sixth in the LMP2 division of the 2015 24 Hours of Le Mans, although Petrov was not involved in that campaign.
Petrov, who picked up one podium in 58 grands prix, has endurance racing experience, having driven in the 2007 Le Mans Series, including an appearance at Le Mans.
The 31-year-old replaces Mikhail Aleshin, who is returning to IndyCar for 2016.