Data on the comparative effectiveness of Diabetes Prevention Programs (DPPs) in the workplace are limited. Between September 2015 and July 2016, employees of the City and County of San Francisco who were at risk for type 2 diabetes (N = 158) were randomly assigned to one of 2 DPP-derived programs recognized by the Centers for Disease Control and Prevention: an in-person YMCA-DPP (n = 78) or an online virtual lifestyle management DPP (VLM-DPP) offered through Canary Health (n = 80). The primary outcome was change in body weight assessed at 6 and 12 months. Follow-up ended in August 2017. Both the YMCA-DPP and VLM-DPP yielded a significant reduction in percentage body weight at 6 months. For the YMCA-DPP, mean percentage change at 6 months was -2.70% (95% confidence interval [CI], -3.91% to -1.48%) and at 12 months was -2.46% (95% CI, -4.24% to -0.68%). For the VLM-DPP, mean percentage change at 6 months was -2.41% (95% CI, -4.07% to -0.77%) and at 12 months was -1.59% (95% CI, -3.51% to 0.33%). The mean between-condition difference at 6 months was -0.25% (95% CI, -2.04% to 1.55%) and at 12 months was -0.84% (95% CI, -3.03% to 1.34%). No significant differences were observed between conditions. The YMCA-DPP had a slightly higher reduction in waist circumference than VLM-DDP at 6 months (mean between-condition difference -2.00 cm [95% CI, -4.24 to 0.25 cm]). Participant engagement, expressed as mean number of completed core program sessions, was significantly higher for the YMCA-DPP than the VLM-DPP. Participants of the YMCA-DPP completed an average of 10.2 sessions (95% CI, 9.0 to 11.4), and participants of the VLM-DPP completed an average of 5.9 sessions (95% CI, 4.7 to 7.1). The adjusted mean between-condition difference was 4.2 sessions (95% CI, 2.54 to 5.99). Both the YMCA-DPP and VLM-DPP yielded weight loss at 6 months, which was maintained at 12 months in the YMCA-DPP. The workplace may be an effective setting to offer DPPs.