He was born in Keithock, near Brechin, and baptised on 2 April 1698, the son of David Edgar and Elizabeth Guthrie.[1][2] He was educated at Marischal College, Abedeen from 1712 to 1714.[1] He married Barbara Rait (1692–1774), daughter of the Reverend William Rait, Incumbent of Monikie, and Isobel Yeaman, and sister of the Right Reverend James Rait, Bishop of Brechin.[1]
His first pastoral appointments were as assistant minister (1727–29) and then Incumbent (1729–32) at Careston, followed by as the Incumbent of Arbroath (1732–65); a post he held until his death.[1] After the Jacobite rising of 1745, Edgar was arrested for not praying for King George II but the case dismissed by the local magistrates after he said that he had "prayed for the King".[1]