Ralph Erskine was the brother of another prominent churchman, Ebenezer Erskine. After studying at the University of Edinburgh, Ralph was ordained assistant minister at Dunfermline in 1711. He homologated the protests which his brother laid on the table of the assembly after being rebuked for his synod sermon, but he did not formally withdraw from the establishment till 1737. He was also present at, though not a member of, the first meeting of the "associate presbytery". When the severance took place over the oath administered to burgesses, he adhered, along with his brother, to the burgher section.
His works consist of sermons, poetical paraphrases and gospel sonnets. The Gospel Sonnets have frequently appeared separately. His Life and Diary, edited by the Rev. D Fraser, was published in 1842.
Erskine was united in marriage to Margaret Dewer, a gentleman's daughter, in 1714.
Erskine's sermons are extant in which he portrayed hell so that his hearers felt they were already there, and then he portrayed heaven's open doors in Christ and admonished his hearers to flee from the wrath to come.
Typical of Erskine's exposition is that of Luke 14:23 on the compelling duty of ministers.