The Wild also received center Cody McCormick in the deal, which sent second-round picks in 2014 and 2016 to the Sabres.
Moulson changes teams for a second time this season after the Sabres acquired him in a deal that sent leading scorer Thomas Vanek to the New York Islanders in October. In his seventh NHL season, Moulson is a three-time 30-goal-scorer, who has 17 goals and 38 points in 55 games this season.
McCormick was a fourth-line role player during his four seasons with the Sabres. He has split this season between Buffalo and Rochester of the AHL and has one goal and five points in 29 games with the Sabres. He's a 10-year veteran.
"We liked our depth. But you never know what can happen in the NHL, and again this team has shown me a lot in the last month and a half," general manager Chuck Fletcher said. "I think they deserve the opportunity to be rewarded with some additional help for the push for the next month here."
The Wild are 14-4-2 since the new year began. They're in seventh place in the Western Conference playoff race.
"We're trying to get to a place where we have at least three lines that can score and play defense," Fletcher said, adding, "We saw this a little bit in the playoffs last year: You need to have more than one line that you can rely on."
McCormick will essentially take the place of Mitchell, who was in his sixth NHL season and second with the Wild after spending his first four years with San Jose. He had difficulty playing a significant role in Minnesota, where he had a goal and nine points in 58 games this season.
Moulson likely will end up on the second line in Minnesota with captain and center Mikko Koivu and perhaps veteran Dany Heatley. That would allow Charlie Coyle to center the third line with Matt Cooke and Nino Niederreiter, a former Islanders teammate of Moulson's. Zach Parise and Jason Pominville, acquired at the trade deadline from the Sabres last season, are skating with Mikael Granlund on the first line.
"I'm always open-minded. I don't have anything set in stone for me," Moulson said. "I'll obviously take it day by day, but the Wild are obviously a great team and I just hope that I can be a part of this team going forward and winning a championship."
Mitchell, who has one more year on his contract at $1.9 million, was traded to clear salary-cap space for next season. So Moulson could be more than a two-month-or-so rental. But the Wild weren't worried about that when they put this deal together.
"He's a guy we think will thrive in the playoff drive that we're undergoing now and if we're able to get into the playoffs to help us there. This is a move made to help us win games right now," Fletcher said.
"Any time you're paying second-round picks for good hockey players, to me it's a really good move," Fletcher added. "We're very comfortable with the gamble."
Also Wednesday, the Sabres sent defenseman Brayden McNabb to the Los Angeles Kings along with forward Jonathan Parker and two second-round draft picks in exchange for forwards Hudson Fasching and Nicolas Deslauriers. In addition, they claimed forward Cory Conacher off waivers from Ottawa.
"I think it's a good day," GM Tim Murray said. "I think the combination of picks that we added and young players that we've added gives us a ton of ammunition now going into the draft."
McNabb had played in 37 games for Buffalo since late 2011, recording one goal and seven assists. He played 12 games for the Sabres this season and 38 for their AHL affiliate in Rochester.
Fasching, listed at 6-foot-2 and 213 pounds, was a fourth-round pick by the Kings last summer. The freshman forward at Minnesota has 12 goals and 15 assists in 31 games.
Deslauriers was a third-round pick in 2009 who moved from defenseman to left wing this season in Manchester for his first professional season. He has a team-leading 18 goals and 21 assists in 60 games for the Monarchs.
ESPN.com's Pierre LeBrun and The Associated Press contributed to this report.