Valencia's blast with J.J. Hardy aboard in the third inning put the Orioles ahead 5-2 and Adam Jones added a solo blast as Baltimore improved to 16-10 on the road this season.
Garcia (1-2) yielded three runs (two earned) on nine hits and no walks over five innings, striking out one.
The 36-year-old right-hander, who spent the last two seasons with the New York Yankees, collected his 153rd career win and first for Baltimore since being recalled from Class AAA Norfolk.
Hardy finished 2-for-4 with two RBI and Jim Johnson helped turn back a late Toronto rally with his 15th save as the O's took a second straight against the Blue Jays.
Toronto starter R.A. Dickey (4-6) was tagged for six runs on nine hits over 6 2/3 innings.