The Reds selected Buchanan's contract from Triple-A Louisville on Saturday.
The Reds acquired Buchanan from Philadelphia on Tuesday in exchange for cash considerations, and the 35-year-old now has the opportunity to pitch in the majors for the first time since 2015. He posted a 4.91 ERA and 1.49 WHIP across 102.2 innings during his time with the Phillies' Triple-A affiliate and will most likely be used as a multi-inning reliever while with the Reds. Evan Kravetz was DFA'd in a corresponding move.