The deal is worth $5.5 million annually, a source told ESPN.com's Pierre LeBrun.
A 21-year-old from Sweden, Ekman-Larsson has been considered Phoenix's top defenseman after the Coyotes took him with the sixth overall pick of the 2009 draft.
Ekman-Larsson played in all 82 games last season, setting career highs with 13 goals and 19 assists. This season, he has three goals in 27 games and leads the Coyotes defensemen with 14 assists and 17 points.
He has 17 goals and 43 assists in 157 career NHL games.
The Coyotes, who are being operated by the league for the fourth straight season, had made signing Ekman-Larsson a priority.