Philip Winchester and Sullivan Stapleton will reprise their roles of Michael Stonebridge and Damian Scott in the action-drama, from Sky / Cinemax.
Robson Green, Dougray Scott and Martin Clunes will join Strike Back for the new season, subtitled Shadow Warfare for UK transmission.
Green is cast as a new member of elite counterterrorism team Section 20, while Hemlock Grove's Scott will play a rogue operative named James Leatherby.
Clunes will debut as former MI6 agent Sebastian Gray, with Rhona Mitra reprising her Strike Back role of Major Rachel Dalton.
Strike Back's latest ten-part run premieres on Friday, August 9 on Cinemax and will air on Sky1 in the UK.