De Slane was born in Belfast, the son of James McGuckin and Euphemia Hughes.

[1] After graduating from Trinity College Dublin, in 1822[1] he moved to Paris and studied oriental languages under Silvestre de Sacy.

[2] The society financed Joseph Toussaint Reinaud and de Slane to prepare a critical edition[3] of Abu'l-Fida (أبو الفداء)'s Arabic geography, Taqwīm al-Buldān (تقويم البلدان)[4] – "Locating the Lands" (1321).

[5][2] Between 1843 and 1846 he was sent on a mission by the French Government to catalogue important documents in the libraries of Algiers and Constantine.

[7][8] He served as Professor of Arabic at the École de langues orientales in Paris and from 1849 also taught Turkish.