The 22-year-old forward, who was a restricted free agent, had 41 points (14 goals, 27 assists) in 71 games as a rookie last season.
"This is something that both parties wanted all along," White said. "I think it was the right move for both myself and Ottawa. I couldn't be more proud to be a Senator for the next six years."
White said having the securtity of a long-term contract can only help his game.
"If anything, I think it's less pressure now because I can just play," he said. "Outplaying this contract is a goal of mine, so every year I just want to get better and continue to improve in any way that I can."
Senators general manager Pierre Dorion said White's ability to play center and wing will help new coach D.J. Smith, who was hired May 23.
"We anticipate that Colin will be a center," Dorion told TSN 1200 radio in Ottawa, "but what we like about him is his versatility, and his speed sometimes shows more coming off the wing, when he can burst and explode, but at the same time, I know D.J. really likes the way [White] plays a 200-foot game and his commitment as a centerman down low, and within D.J.'s system, these centermen are really going to have to bear down in their own end, and Colin is very good at doing that."