The 38-year-old Tkachuk played in his 1,200th game Monday night but was scratched Wednesday night at Chicago because of a lower-body injury, a day after the Blues were eliminated from the playoff race.
Tkachuk has 1,063 points on 538 goals and 525 assists and 2,219 penalty minutes. In January, the five-time All-Star and four-time U.S. Olympian became the fourth player in NHL history with 1,000 points and 2,200 penalty minutes.
Tkachuk has 13 goals and 17 assists in 66 games this season. He has played for the Blues since a trade from the Phoenix Coyotes in 2000-01, aside from a brief stint with the Atlanta Thrashers at the end of the 2006-07 season.
"I have been privileged to have a long career in this terrific league and play for first-class organizations," Tkachuk said.
A native of Melrose, Mass., Tkachuk was a first-round pick of the Winnipeg Jets in 1990. In his prime he was one of the NHL's top power forwards and peaked with 52 goals and 228 penalty minutes in 1996-97.
"Keith is a true warrior who had an excellent career and I was hoping this day would never come," team president John Davidson said. "The NHL is losing an individual who gave a lot of time and dedication to the game."