On the rebuilding Senators, the 22-year-old White stepped into the top center position and had a solid season with 14 goals and 27 assists. He also quarterbacked the team's second power-play unit.
White will be counted on to play a significant role next season as the team continues its rebuild.
"We've identified Colin as one of our core young players who will help drive our team's success in both the short and long term," Senators general manager Pierre Dorion said in a statement. "Colin plays the 200-foot game that is so coveted in today's NHL. He can skate, play on both special teams, and is a character player and leader who loves hockey and this city. While he is coming off a season where he finished among rookie leaders in many categories, we also know he is just scratching the surface of his potential in this league. We're very happy that Colin will be a Senator for the next six years."
White signed a three-year, entry-level contract in April 2017 with a cap hit of $925,000 to forgo his final two years at Boston College. He was a restricted free agent this offseason.
He was one of seven Senators players to issue an apology in November after they were recorded criticizing the team's poor play and an assistant coach while riding in an Uber. The conversation was then published online.