BACKGROUND: Meta-analyses have identified promising behavior change techniques (BCTs) in changing obesity-related behaviors from intervention descriptions. However, it is unclear whether these BCTs are used by intervention participants and are related to outcomes. PURPOSE: The purpose of this study is to investigate BCT use by participants of an intervention targeting physical activity and diet and whether BCT use was related to behavior change and weight loss. METHODS: Intervention participants (N = 239; 40-69 years) with recently diagnosed type 2 diabetes in the ADDITION-Plus trial received a theory-based intervention which taught them a range of BCTs. BCT usage was reported at 1 year. RESULTS: Thirty-six percent of the participants reported using all 16 intervention BCTs. Use of a higher number of BCTs and specific BCTs (e.g., goal setting) were associated with a reduction in body mass index (BMI). CONCLUSIONS: BCT use was associated with weight loss. Future research should identify strategies to promote BCT use in daily life. ( TRIAL REGISTRATION: ISRCTN99175498.).