He was appointed governor of Cardigan Castle by Laugharne in 1644 as soon as it was captured and successfully defended it against a Royalist attack led by Sir Charles Gerard, 1st Earl of Macclesfield.
In 1646 he was governor of Tenby Castle and by 1648 he was deputising for Laugharne when he was called to London and held command of all the forces in West Wales at the time of the order for supernumeraries to lay down their arms.
Rice Powell followed John Poyer's lead and resisted this order, making a joint declaration in favour of the Royalist cause.
Powell now led his forces to seize Swansea, then Neath before advancing into the Vale of Glamorgan with Royalists rising in support en route, with Cardiff as their aim.
Powell fled back to Pembrokeshire and Tenby castle where he was pursued and after a brief siege was persuaded to an unconditional surrender after which he was Court Martialed and sentenced to death.