Group therapy has the potential to reach more people seeking treatment at the same time while achieving similar success rates as individual therapy. We examined whether adding group therapy (behavioral activation) before individual therapy shortens the duration of therapy while being no less effective than pure individual therapy. In a cognitive behavioral therapy (CBT) outpatient clinic, we analyzed data from N = 290 patients diagnosed with depression. While comparing group plus individual versus pure individual therapy, we controlled for systematic differences using propensity score matching. Patients receiving group therapy prior to individual therapy waited significantly shorter for treatment and needed fewer individual sessions. Linear mixed model analysis of depression scores revealed a significant interaction between time and condition, indicating that patients in the combination treatment improved faster than patients who received individual therapy only. Prior group treatment with behavioral activation increases the efficiency of outpatient CBT for depression.