Mortimer, Edmund (1394–1425), 5th earl of March and 8th earl of Ulster , was eldest son of Roger (qv), 4th earl of March, and Eleanor, daughter of Thomas Holland, earl of Kent. He was the third generation of his family to succeed to his father's titles while still a minor. He inherited a potential claim to the throne, and because of this was kept under close scrutiny by Henry IV. March was put forth as the rightful king in several rebellions during Henry's reign, but developed a loyalty to the Lancastrian dynasty. In 1407 his marriage was granted to Queen Joan, who arranged a marriage with Anne, daughter of Edmund Stafford, earl of Stafford. In 1409 his custody was granted to Henry, prince of Wales. He was granted livery of his lands by Henry V in 1413, and in April 1413 was made a knight of the Bath.
In 1415 he revealed a plot to place him on the throne to Henry V, who accepted his protestations of innocence. He joined the king on his French expedition later that year, fell ill at Harfleur (October 1415), and returned to England. He was one of the two captains of an expedition to relieve Harfleur in August 1416, and in July 1417 he was given the powers of an admiral. The following year he took part in the campaign to conquer western Normandy, was appointed lieutenant of Normandy (July), and served at the sieges of Rouen and Meulun. He travelled to England with Henry V and Queen Catherine in February 1421, returned to France in June, and remained there till the king's death (August 1422). He was appointed to the regency council of Henry VI in December that year.
March was appointed lieutenant of Ireland (May 1423) in an attempt to end the growing factionalism in the Irish administration, but did not go to Ireland till forced by a growing quarrel with Humphrey, duke of Gloucester. He appointed two deputies, Edward Dauntsey (qv), bishop of Meath, and James Butler (qv), 4th earl of Ormond, to govern in his place, not arriving in Ireland till September 1424. As March's deputy, Ormond had campaigned in Ulster to restore the traditional authority of the earls of Ulster, and several Gaelic magnates were present in Trim, having recently submitted to the lieutenant, when March died suddenly in January 1425. He was buried in Clare Abbey, Suffolk; as he died without children, his lands and titles passed to his nephew Richard, son of his sister Anne and Richard, earl of Cambridge, the future duke of York.