Born in Dublin, Longford was the eldest son of William Pakenham, 4th Earl of Longford, and his wife the Hon. Selina (née Rice-Trevor), and succeeded in the earldom on his father's death in 1887. He served in the Life Guards, achieving the rank of Colonel, and also held the honorary post of Lord-Lieutenant of County Longford from 1887 to 1915. In 1901 he was made a Knight of the Order of St Patrick. In Dublin, he was a member of the Kildare Street Club.