Marmol waived his no-trade clause to accept the deal.
"I like the team, it wins every day," Marmol said. "With all the players here, it's a good team. How can I say no? Better than Chicago."
He was tested immediately on Tuesday, relieving starter Chris Capuano in the fifth and allowing three runs on four hits, including a Jose Reyes homer, in 1 2/3 innings in the Dodgers' 10-9 come-from-behind win over the Blue Jays.
"You can tell he gets going fast and he gets going everywhere," Dodgers manager Don Mattingly said. "He gave up a home run but got three outs. A little good, a little bad."
Marmol agreed to pitch in the Minor Leagues to work on his mechanics with pitching coordinator Rafael Chaves, who accompanied him to Toronto. He had a 3.60 ERA in five appearances.
"I accept, because I need it," Marmol said. "Now I'm standing up straight, getting command of my fastball. The slider is always there. Command of the fastball, I think. I'll be all right with the slider."
The club hopes Marmol, 30, can regain enough of his past form to be used in middle and setup relief, with Kenley Jansen remaining the closer. Marmol said he wouldn't object to a setup role.
"It'll be fine," he said. "Just give me the ball."
Mattingly said Marmol needed a change of scenery, "as much as anything." He'll take over the innings pitched by Dominguez -- most often the sixth or seventh. Dominguez tweaked a quad muscle coming off the mound on Monday as A.J. Ellis caught Jose Reyes' foul pop to end the sixth inning.
"Jose did a pretty nice job," Mattingly said. "He's got things he can work on -- command, getting ahead, getting the breaking ball over. But I like his temperament, the way he handles himself. I think he'll be really good."
Before he was designated by the Cubs, Marmol went 2-4 with a 5.86 ERA in 31 games with 32 strikeouts, but he also had 21 walks and six home runs allowed.
Marmol began the season as the Cubs' closer, but he lost the job after the first week to Kyuji Fujikawa. However, the Japanese pitcher had elbow problems and eventually required Tommy John surgery. In a strange twist, Kevin Gregg replaced Marmol, who had replaced Gregg as the closer in 2009. In a stranger twist, Gregg was released by the Dodgers at the end of Spring Training.
Marmol was an All-Star in 2008, and in 2010-11, he compiled 72 saves. He will be a free agent after this season.