Behavioral activation (BA) is an empirically-supported treatment for major depressive disorder that seeks to increase overt behaviors as a way of countering withdrawal and passivity that often occurs during it. While some variants of BA focus more on increasing activities to elevate mood, more recent ones have placed more emphasis on instigating overt actions congruent with personal values. To date, no research has compared the relative efficacy of these two BA protocols nor their possible differential mechanisms of action. This project addressed this omission by utilizing a single-subject experimental design in which participants experiencing clinical depression received an 8-week treatment protocol of mood-based (n = 6) or value-based BA (n = 8) following 3-5 weeks of baseline. Both protocols produced equivalent statistically and clinically significant outcomes on symptoms of depression, anxiety, and quality of life that were maintained through 2 months of follow-up. However, mediational analyses suggested that they did so through differing processes. Although enhanced overall mood mediated improved outcomes for both groups, it did so to a relatively greater degree in the value-based protocol. In addition, increased enjoyment from, and importance associated with engaging in activities, were mechanisms of action unique to the value-based group. Limitations of this study, implications of its findings for clinical practice, and recommendations for future research are discussed.