St. Louis, 38, has played in Tampa Bay for the past 12 seasons and is the last player remaining from the Stanley Cup-winning team of 2003-04. He is coming off a season in which he became the oldest player in NHL history to lead the League in scoring.
"Our discussions regarding a new captain began in June and we're very excited to make this announcement tonight," coach Jon Cooper said in a statement. "Marty embodies everything a captain should be. The captaincy is one of the highest honors in hockey and Marty is well-deserving. We have a great group of leaders on this team and I'm sure Marty will receive plenty of support moving forward."
St. Louis is the Lightning's all-time leader in points (892), assists (556) and shorthanded goals (28). He ranks second for games played (910), goals (336), power-play goals (87) and game-winning goals (59). He won the Hart Trophy as the NHL's Most Valuable Player in 2003-04, is a two-time winner of the Art Ross Trophy as the NHL's leading scorer and a three-time recipient of the Lady Byng Trophy, given for skillful and gentlemanly play.
St. Louis will wear the "C" for the first time on Thursday when the Lightning open their season on the road against the Boston Bruins.
"I don't think it's a different pressure. It's the same pressure. I want to help my team win," St. Louis said after being given the captaincy.