Title(s): Marshal of the East-mark
Led 4 companies in both the First and Second Battles of the Fords of Isen.
Led the éored that Éowyn as Dernhelm joined, along with Meriadoc Brandybuck, at the Battle of Pelennor Fields.
Material from Unfinished Tales, Part 3, Ch V, The Battles of the Fords of Isen
From his words to Théoden: "We need no further guidance," said Elfhelm; "for there are riders in the host who have ridden down to Mundburg in days of peace. I for one."
Book 5, Ch 5, The Ride of the Rohirrim, RoTK, LOTR
Thus we know he has traveled to Minas Tirith before the war.
Led the battle against the orcs in Anórien, while the force under Aragorn went to the Black Gate. "...the main strength of the Rohirrim that remained horsed and ready to fight, some three thousand under the command of Elfhelm, should waylay the West Road against the enemy..."
Book 5, Ch 9, The Last Debate, RoTK, LoTR
Present at the coronation of Aragorn as King Elessar.
Book 6, Ch 5, The Steward and the King, RoTK, LoTR