In October 1838, he was admitted to deacon's orders, and after his return from Italy he took charge of the episcopal congregation at Forres, and was ordained a presbyter in the autumn of 1841.
In 1847, he was consecrated bishop of the newly united Diocese of Argyll and The Isles, the duties of which position he discharged till his death.
Though hampered by poor health, he worked cheerfully, and his personal charm and Catholic sympathies gradually won him a prominent position.
His own theological position had close affinity with that of Thomas Erskine of Linlathen and Frederick Denison Maurice; but his opinions were independent.
Ewing's daughter Margaret Nina married Alexander Crum printer and MP in 1863.