The 33-year-old center is in the final season of a five-year contract he signed with the Capitals on Feb. 10, 2018, and can become an unrestricted free agent after the season.
Eller has 16 points (seven goals, nine assists) in 60 games this season.
"Solid, big, strong third-line center," Avalanche coach Jared Bednar said Wednesday. "That's what he is. Penalty-killer, good on draws, lots of experience. I'd say this is good pickup.
"We need help in the middle of the ice, and with guys like Darren] Helm and [Gabriel Landeskog]*
"I expect him to go do what he's done for the Caps and Canadiens and his whole career," Bednar said. "He's a veteran guy, right? So normally when you bring in veteran guys, you're acquiring [them] for a reason.
"My conversation is like, 'That's why we got you, to do what you've been doing within our group now.' Brush him up on some of the details of our game because it may be different. 'Don't think too much, just trust your instincts and go play,' if he gets in and is playing tonight. And then we'll sit down with him over the next couple of days and prepare for the weekend. But he brings a lot of strengths that we need, and that's why we acquired him. And we'd like him to continue to do those things."
Eller flew to Denver and made his Avalanche debut in a 7-5 loss to the New Jersey Devils later on Wednesday. He was minus-1 in 14:28 of ice time.
"I literally got here like 15 minutes before I was supposed to go on the ice, so I felt like I was going to have a little more time. I wanted to get in as quick as possible," Eller said. "[It was] certainly not my best game or for the team, but now we're started and I'm excited to be part of this team. [I am] really, really pumped to be here.
"I think it's such a great opportunity. It is a special opportunity to be on a team being in a playoff spot and have the history here."
The Avalanche (34-19-5) are third in the Central Division, one point behind the Minnesota Wild and four points behind the Dallas Stars.
Colorado previously acquired defenseman Jack Johnson from the Chicago Blackhawks on Sunday for defenseman Andreas Englund. Johnson won the Cup with Colorado last season.
"Some of these players that we're bringing in are veteran guys that have been there, done that," Bednar said. "Still hungry to win. They have won. It's good to have. You need that experience, and you need those players that are capable of playing under that type of pressure and that type of intensity."
The Capitals (29-27-6) are three points behind the Pittsburgh Penguins for the second wild card into the playoffs from the Eastern Conference. On Tuesday, they traded forward Marcus Johansson to the Minnesota Wild, and defenseman Erik Gustafsson to the Toronto Maple Leafs for defenseman Rasmus Sandin.
Washington sent defenseman Dmitry Orlov and forward Garnet Hathaway to the Boston Bruins in a three-team trade on Feb. 23.
NHL.com independent correspondent Ryan Boulding contributed to this report
