Guernsey was born in Mullingar, Co. Westmeath, studied briefly as a boy with the well-known Italian opera composer Saverio Mercadante at Lisbon during 1827–8, returning to Ireland probably during the early 1830s to work in Cork and Dublin.
Of his early career a newspaper correspondent wrote in 1858: "Mr Wellington Guernsey [...] was, I believe, born in Ireland, his father having been master of a military band, and was formerly in the employment of Messrs. Robinson and Bussell, music-sellers, Westmoreland Street.
He subsequently obtained, during the Crimean war, a majority in the Turkish Contingent, from which he was removed by General Vivian for gross misconduct.
He has since been hanging about the theatres in London, gaining a livelihood composing waltzes, &c., which were very popular, and which were constantly performed by her Majesty's private band.
In 1847 he became musical director of the Olympic Theatre in London, but by the early 1850s he must have embarked on his military career which took him to Turkey in 1855, the Crimea in 1856 and to Paraguay and Brazil in 1857.
He stopped composing piano galops and waltzes by 1862, and some of his Ireland-inspired songs like The Boatman of Kinsale (1865) and The Green Moss (1869) did not fetch the same public attention as his pre-1850 music.