Offshore macroalgae biomass production is a promising, yet challenging, pathway to provide feedstock for biorefineries. In this work, a device and a process for dewatering offshore grown biomass of the green macroalgae Ulva sp. using high-voltage pulsed electric fields (PEF) was developed. Ulva sp. was cultivated attached to fish cages 15 km offshore. Increasing the applied voltage from 250 V to 500 V and invested PEF energy from 9.3 ± 0.4 J g-1 FW to 54.6 ± 0.2Jg-1 FW increased the extracted water from 0.033 ± 0.006 g Water g-1 FW to 0.150 ± 0.031 g Water g-1 FW. The energy consumption to achieve similar moisture content with air convection drying was lower by 78.73 ± 10.41 (JgFW-1) for 250 V and 339.31 ± 48.01 (JgFW-1) for 500 V, pulse duration 50 µs, pulse number 50, pulse repetition frequency 3 Hz. PEF leads to biomass compression of 8.45 ± 1.72% for 250 V protocol and 25.66 ± 2.53% for 500 V protocol. In addition, PEF leads to the reduction of water diffusivity of 18-19% in the treated biomass, reducing air drying kinetics.