In September 1833, after more than four years in Western Australia, Irwin returned to England, partly to give an account to the Colonial Office of the events that had occurred in the colony while it was under his charge. While there, he published The State and Position of Western Australia, the first published account of the colony. He also sought religious assistance for the colony, resulting in the arrival of the colony's first missionary, Louis Giustiniani, in 1836. He married his wife Elizabeth Courthope, sister of auditor-general of Western Australia in December 1836. In 1837, having been promoted to Major, he returned to Western Australia, and was made permanent Commandant of the Western Australian Forces. He was further promoted to Lieutenant-Colonel in 1845.
