The Commonwealth , or Commonwealth of England , was the period from 1649 onwards when England , along later with Ireland and Scotland , was ruled as a republic following the end of the Second English Civil War and the trial and execution of Charles I . The republic 's existence was initially declared through `` An Act declaring England to be a Commonwealth '' , adopted by the Rump Parliament on 19 May 1649 .
After the execution of Charles I on January 30 , 1649 , the Commonwealth was declared ( An Act declaring England to be a Commonwealth ) by the Rump Parliament on May 19 , 1649 .