Background <p>This study evaluated the impact of a fully subsidized behavioral weight management program (WW; formerly WeightWatchers^®) among adults with type 2 diabetes or prediabetes enrolled in the 1199SEIU Benefit Funds, a self-administered labor–management fund providing health coverage to over 360,000 union members, retirees, and their families.</p> Methods <p>Using a quasi-experimental mixed-methods design, we analyzed clinical claims data and focus group transcripts. Quantitative outcomes included HbA1c, body mass index (BMI), and program engagement. A one-to-one propensity score–matched control group was constructed to compare pre-post changes over a minimum six-month exposure period. Qualitative analysis explored barriers and facilitators to program participation.</p> Results <p>Among participants living with type 2 diabetes, those enrolled in WW experienced significant reductions in BMI and significant improvements in HbA1c control, while those with pre-diabetes demonstrated BMI reductions and no significant change in HbA1c levels. Higher engagement with WW, particularly through food tracking, activity tracking, and workshop participation, was associated with greater BMI reductions. GLP-1 medication use in the study sample was independently associated with reductions in HbA1c, and the combined effect of WW participation and GLP-1 use on BMI warrants further study given that interaction effects were non-significant in adjusted models. Qualitative findings highlighted key barriers and facilitators to engagement, including time constraints, family dietary preferences, and program accessibility.</p> Conclusion <p>These findings provide real-world evidence supporting employer- or payer-sponsored behavioral weight management programs as a strategy to improve diabetes-related outcomes. Integration with pharmacotherapy warrants further investigation.</p>