The Senators announced the agreement on Wednesday. Wideman was selected by Ottawa in the fourth round of the 2009 draft and was eligible to be a restricted free agent this summer.
Wideman has scored five goals, which rank third among NHL rookie defensemen this season. He also has four assists for nine points in 44 games.
Last year, Wideman was named the American Hockey League's best defenseman after leading the league's blue-liners with 61 points while playing for Binghamton.