Betancourt, who saved a career-high 31 games for the Rockies in 2012, missed all of last season recovering from Tommy John surgery and signed a minor- league deal with Colorado in January.
The 11-year vet earned a spot with a strong spring, yielding just one run and striking out nine batters over 7 2/3 innings.
Betancourt turns 40 on April 27 and re-joins a bullpen that already contains the oldest active player in the majors, 42-year-old closer LaTroy Hawkins.
His addition came at the expense of left-hander Rex Brothers, optioned to Albuquerque Wednesday after struggling all throughout spring training.
Brothers, who saved 19 games after replacing an injured Betancourt as Colorado's closer in 2013 and posted a 1.74 ERA that season, walked six batters and allowed seven runs in 7 2/3 innings in eight Cactus League appearances.
The 27-year-old had a disappointing 2014 campaign as well, finishing with a career-worst 5.59 ERA over 74 games.
Outfielder Brandon Barnes, who played in 132 games and batted .257 with eight homers with the Rockies last season, was also sent to Albuquerque among Wednesday's moves.