Dallas waived reserve point guard Facundo Campazzo, whose contract is nonguaranteed, to create an open roster spot for Walker.
The Mavericks officially announced Walker's signing on Tuesday.
Speaking before Tuesday night's game against Golden State, coach Jason Kidd said the club hoped to get Walker on the court for practice Wednesday. He hasn't played since Feb. 16.
Dallas signed Walker in the midst of a four-game losing streak and a stretch of seven games in 11 days before the next time the team gets multiple days off.
"The train doesn't stop,'' Kidd said. "We'll get him caught up to speed. He's a vet. He's been in this league. And we'll hopefully put him in a position that he can be successful.''
Walker, 32, a four-time All-Star whose career has been derailed by knee issues, has been a free agent since being waived by the Detroit Pistons in mid-October. He averaged 11.6 points and 3.5 assists in 37 games last season for the New York Knicks, who traded him to the Pistons on draft night in a cost-cutting move that helped create the salary-cap space for New York to sign former Mavericks guard Jalen Brunson in free agency.
Doncic is leading the NBA in scoring with 33.1 points per game, but opponents are increasingly trapping and double-teaming him to force the ball out of his hands, daring his teammates to beat them. The Mavs have struggled to score when Doncic rests, averaging only 104.0 points per 100 possessions when he is off the floor. They are 0-6 when he doesn't score 30 points, including a loss to the Houston Rockets when Doncic did not play due to rest.
The Mavs attempted to sign Walker to a maximum contract in 2019 free agency, but he opted to accept an identical offer from the Boston Celtics. He averaged 22.8 points and 5.6 assists in two injury-marred seasons for the Celtics, who traded Walker and a first-round pick to the Oklahoma City Thunder for Al Horford. Walker received a buyout from the Thunder, allowing him to sign a two-year deal with the Knicks.
Walker's tenure with the Knicks unofficially ended during the All-Star break, when the team announced that he would no longer play for them. He sat out the final two months of the season.
Walker has been training in Florida this season while awaiting an opportunity to sign with an NBA team.
"I'm just making sure I'm right, making sure I'm ready, making sure I'm ready for whenever somebody gives me that call," Walker said during an appearance on "The Woj Pod" earlier this month. "I just know that I have the ability to help someone, to help a team. I know I can still play basketball at a high level."
Information from The Associated Press was used in this report.