If wave and tidal energy devices are to become a significant contributor to the electricity generation mix, their environmental impact and energy and carbon footprints need to be added to the traditional technoeconomic assessment. This paper presents the life cycle carbon and energy study of an array of ten tidal stream turbines equipped with the innovative power take-off developed, built and tested under the European H2020 project TiPA. A ‘cradle-to-grave’ evaluation was performed, taking account of all energy inputs and CO2 emissions in the fabrication, transport, installation, lifetime maintenance and decommissioning (including recycling). The calculated energy and carbon intensities were at 445 kJ/kWh and 29.2 g CO2/kWh, respectively. Under relatively conservative assumptions, the energy payback period for the simulated array was calculated at 30 months, while the carbon payback period was 25 months. The obtained results on intensities and payback periods were found to be competitive with those of existing studies on alternative marine energy concepts, and low relative to the conventional nuclear or fossil-fuelled generation. Given the early developmental stage of the technology, these results are promising, and could be further improved by considering alternatives to steel as a structural material or by improving the environmental performance of the foundation element.