BACKGROUND: Sedentary behaviour is a risk factor for type 2 diabetes and cardiovascular disease. OBJECTIVES: The aims of this work were to systematically review the effects of workplace sedentary behaviour reduction interventions on cardiometabolic risk markers (primary aim) and identify the active behaviour change techniques (BCTs) by which these interventions work (secondary aim). METHODS: A systematic search of 11 databases for articles published up to 12 April 2019 yielded a total of 4255 unique titles, with 29 articles being identified for inclusion. Interventions were rated as very promising, quite promising or non-promising based on their effects on cardiometabolic risk markers compared with baseline and/or a comparison arm. Interventions were coded for BCTs used. To assess the relative effectiveness of BCTs, a promise ratio was calculated as the frequency of a BCT appearing in all promising interventions divided by its frequency of appearance in all non-promising interventions. RESULTS: A narrative synthesis included 29 published studies of varying study design and comprised of 30 interventions. Risk of bias was high for blinding and allocation concealment, moderate for random sequence generation, and low for outcome assessment. Nine interventions were very promising, 11 were quite promising, 10 were non-promising, and 10 active control groups did not experience cardiometabolic changes. Significant sedentary behaviour reductions were present in all but five studies where cardiometabolic risk markers improved. The BCTs of social comparison, problem solving, demonstration of the behaviour, goal setting (behaviour), behaviour substitution, and habit reversal, demonstrated moderate to high promise ratios. CONCLUSIONS: Workplace interventions show promise for improving cardiometabolic risk markers. The BCTs with the greatest promise of cardiometabolic risk marker improvements included social comparison, those related to individual habits, and behaviour goals. REGISTRATION: This systematic review was prospectively registered in PROSPERO (CRD42017072427).