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.
Apparently the rebels has been assured of Royalist support for their stance and at Carmarthen Powell's forces met those of Colonel Fleming and Colonel Horton, who attempted to bring Powell's force to battle near Llangathen resulting in a skirmish during which Fleming in retreat was shot and Horton was forced to withdraw as far as Brecon to resupply.
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.
Horton headed south from Brecon rapidly and caught Powell's force camped at St Fagans within view of Cardiff and drew them to battle at what became known as the Battle of St. Fagans in May 1648. Laugharne returned in time to retake command but was routed by Hortons force in a decisive victory.
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.
In 1649 he was offered a Pardon and following the Restoration he was released. He last comes to notice in 1665 appealing to Charles II of England for payment of debts Powell accrued in the Royalist cause. There is no record of his debts being paid.