"The St. Louis Blues realize how integral Andy is to the future of our organization," team president John Davidson said. "He's a top-line centre who will play a major role in the development of our team."
The 31-year-old McDonald is in his eighth NHL season. He has missed the past 35 games with a broken left leg, but practised Monday and could play Tuesday when the Blues host Vancouver. In 16 games before the injury, he led the Blues with 18 points, including six goals and 12 assists.
"I've been really itching to get back in," McDonald said. "I feel like now I'm at the point where I can contribute."
McDonald has 20 goals and 54 points in 65 games with St. Louis since he was acquired from Anaheim in the middle of last season. He was part of the Ducks team that won the 2007 Stanley Cup.
In 456 career games, McDonald has 112 goals and 201 assists for 313 points, along with 206 penalty minutes.
McDonald said his priority was to stay in St. Louis.
"I'm excited with the direction that this franchise is going, and we have nothing but good things ahead of us," he said. "Negotiations started a while back and I really wanted to re-sign with St. Louis."
It's been a rocky road to this point. After 25 straight post-season appearances, the Blues haven't made the playoffs since 2004.
This season, they're still in the hunt. St. Louis is 6-1-3 over the last 10 games but still has the fewest points in the closely bunched bottom tier of the Western Conference. Going into play Monday night, St. Louis was six points behind Vancouver and Edmonton for eighth place.
McDonald was hurt on Nov. 16 when he crashed into the corner boards late in the first period of a 3-2 shootout loss to the Montreal Canadiens.
It is one of several injuries to key players for the Blues this season. Forward Paul Kariya has been sidelined with a hip injury since Nov. 5. Defenceman Erik Johnson, the overall No. 1 pick of the 2006 draft, is out the entire season after injuring his knee in a pre-training camp golf outing accident. Another defenceman, Eric Brewer, has been out with a back injury since Dec. 13, and it's uncertain when he'll return.
McDonald, a native of Strathroy, Ont., originally signed as an undrafted free agent by Anaheim in 2000.