The team announced the deal, which will carry an annual value of $1 million for the 2018-19 season, in a release Sunday morning.
Wideman, 28, had three goals and five assists in 16 games during the 2017-18 season.
He suffered a torn hamstring during a game against the Pittsburgh Penguins on Nov. 16 and required season-ending surgery.
"We’re happy to have Chris back for next season," said general manager Pierre Dorion. "We felt that last year he was trending to become the active, puck-moving defenceman that will complement our style of play.
"We certainly missed Chris after his injury and he has since been cleared to resume full athletic competition with no restrictions. He’s having a great summer of training and we know he’s excited to get to Ottawa for training camp."
Wideman has 14 goals and 24 assists in 156 career NHL games, all with Ottawa. He has a goal and three assists in 15 playoff games.
Wideman was the Senators’ fourth-round selection (100th overall) in the 2009 NHL draft.
He was scheduled to become an unrestricted free agent on July 1.