Ayala, 36, had a 3.27 ERA (121 ERA+) with a 58.9 percent ground ball rate in 33 innings for the Orioles and Braves. He missed close to three months with an anxiety disorder.
Washington has a stacked setup crew led by Drew Storen, Tyler Clippard, Craig Stammen and Ryan Mattheus. Jerry Blevins was acquired earlier this winter to be the primary lefty.
Ayala originally broke into the big leagues with the Expos back in 2003. He spent the 2003-08 seasons as the team's primary setup man, posting a 3.33 ERA (131 ERA+) in 332 1/3 innings.