The deal is worth $1.6 million and carries an annual value of $800,000 trough the 2017-18 season.
Wideman has five goals and nine points in 44 games with the Senators this season. The 26-year-old rookie ranks third among first-year defencemen in goal scoring.
Wideman currently earns an NHL salary of $600,000 according to generalfanager.com.
The former fourth-round pick (100th overall) was the 2014-15 recipient of the Eddie Shore Award as the AHL's best defenceman. He totaled 19 goals and 61 points in 75 games with the Binghamton Senators.