Cyanobacteria are promising chassis strains for the photosynthetic production of platform and specialty chemicals from carbon dioxide. Their efficient light harvesting and metabolic flexibility has allowed a wide range of biomolecules, such as the bioplastic polylactate precursor D lactate, to be produced, though usually at relatively low yields. In order to increase photosynthetic electron flow towards the production of D-lactate, we have generated several strains of the marine cyanobacterium Synechococcus sp. PCC 7002 (Syn7002) with deletions in genes involved in cyclic or pseudo-cyclic electron flow around photosystem I. Using a variant of the Chlamydomonas reinhardtii D-lactate dehydrogenase (LDHSRT 25 , engineered to efficiently utilize NADPH in vivo), we show that deletion of either of the two flavodiiron flv homologues (involved in pseudo-cyclic electron transport) or the Syn7002 pgr5 homologue (proposed to be a vital part of the cyclic electron transport pathway) is able to increase D-lactate production in Syn7002 strains expressing LDHSRT 29 and the Escherichia coli LldP (lactate permease), especially at low temperature (25 °C) and 0.04% (v/v) CO2, though at elevated temperatures (38 °C) and/or high (1%) CO2 concentrations the effect was less obvious. The Δpgr5 background seemed to be particularly beneficial at 25 °C and 0.04% (v/v) CO2, with a nearly 7-fold increase in D lactate accumulation in comparison to the wild-type background (≈1000 vs ≈150 mg/L) and decreased side effects in comparison to the flv deletion strains. Overall, our results show that manipulation of photosynthetic electron flow is a viable strategy to increase production of platform chemicals in cyanobacteria under ambient conditions.