Hallam was born in London, son of a historian, Henry Hallam. In 1828, he went up to Trinity College, Cambridge, where he met Tennyson. Both joined a group known as the "Apostles". Their shared interests led to a close friendship, and Arthur became engaged to Tennyson's sister, Emilia Tennyson. While travelling abroad with his father, he died suddenly at Vienna, of a brain haemorrhage.
Tennyson not only dedicated one of his greatest poems to Hallam, but named his elder son after his late friend.