Josias Leslie Porter (1823–1889) was an Irish Presbyterian minister, missionary and traveller, who became an academic administrator.
Born on 4 October 1823, he was youngest son of William Porter of Carrowan, parish of Burt, County Donegal, a farmer, and Margaret, daughter of Andrew Leslie of Drumgowan in the same parish. After being educated privately, between 1835 and 1838, by Samuel Craig, presbyterian minister of Crossroads, County Londonderry, and then at a school in Derry, he matriculated in the University of Glasgow in 1839, with a view to entering the ministry of the Irish presbyterian church. He graduated B.A. in 1841, and M.A. in 1842. In November 1842 he went to the university of Edinburgh, where he studied theology under Thomas Chalmers, continuing also to the Divinity Hall of the Free Church of Scotland, again to study under Chalmers.
Porter was licensed to preach by the presbytery of Derry on 20 November 1844. He was ordained on 25 February 1846, and until 1849 was minister of the presbyterian congregation of High Bridge, Newcastle-on-Tyne. He was then sent to Damascus as a missionary to the Jews by the board of missions of the Irish presbyterian church. He reached Syria in December 1849, and remained there for ten years.
In 1859 Porter returned home on furlough, and in July 1860 was appointed professor of biblical criticism in Assembly's College, Belfast, in succession to Robert Wilson. In 1864 he received the degrees of LL.D. from Glasgow and D.D. from Edinburgh. In 1867, on the death of Professor William Gibson, he became secretary of the college faculty at Belfast, and was an effective fundraiser. Porter, from the time of his appointment as professor, took a leading part in the work of the church courts, and in 1875 was elected Moderator of the General Assembly. During his tenure of the office he initiated a fund which provided manses for many congregations.