Wideman's new deal is worth an average of US$5.25 million annually.
Calgary obtained Wideman for defenceman Jordan Henry and a 2013 fifth-round draft pick.
The Flames also announced they've re-signed forward Blake Comeau to a one-year, US$1.25-million deal. Comeau had five goals and 10 assists in 58 games with Calgary after being claimed off waivers from the New York Islanders in November.
Wideman has 67 goals and 184 points in 535 career NHL games with St. Louis, Boston, Florida and Washington. The six-foot, 200-pound native of Kitchener, Ont. had 11 goals and 35 assists in 82 games with the Capitals last year.
Note to readers: This is a corrected story. An earlier version reported that Wideman had 345 assists last season.