[1] In 1215, Gilbert and his father were two of the barons who made Magna Carta sureties and championed Louis "le Dauphin" of France in the First Barons' War, fighting at Lincoln under the baronial banner.

He was taken prisoner in 1217 by William Marshal, whose daughter Isabel he later married on 9 October, her 17th birthday.

In 1228, he led an army against the Welsh, capturing Morgan Gam, who was released the next year.

He then joined in an expedition to Brittany, but died on his way back to Penrose in that duchy.

Gilbert de Clare had six children by his wife Isabel Marshal, great-grandmother of King Robert the Bruce: His widow Isabel later married the King of the Romans & Earl of Cornwall, Richard Plantagenet, of the House of Plantagenet.