The deal is worth $28 million in total for an average cap hit of $5.6 million, a source told ESPN.com.
Pominville, who would have become an unrestricted free agent after the season, had expressed a desire to sign the extension before the season began.
The Wild acquired Pominville, 30, from the Buffalo Sabres at April's trade deadline. He had nine points (four goals, five assists) in 10 games after the trade.
Minnesota opens at home against the Los Angeles Kings on Thursday night.