DeLeon had spent the last six years with D.C., racking up more than 200 games with the franchise. He joins Toronto in the MLS Re-Entry Draft after United declined his contract option ahead of 2019.
Generally utilized as a wide midfielder for the majority of his career, DeLeon can also operate as a full-back if needed, a role in which he was used almost exclusively in the 2018 season. However, he missed 19 games this term from June until early October with a knee injury.
The 28-year-old tweeted Friday afternoon to express his thanks to Toronto president Bill Manning, general manager Tim Bezbatchenko, and head coach Greg Vanney.