This was originally considered part of Corporation Street. The northern section features in Matier's Belfast Directory for 1835 under the separate name of Garmoyle Street. For a street in Sailortown, it is very apt that is named from a local maritime feature.
The name applied to a spot in Belfast Lough known in English as Garmoyle (sometimes Carmoyle) or the Pool of Garmoyle. This was a deep water pool which existed until the 1840s, located on a bend at the neck of the harbour channel. It was the limit of travel for many large vessels with a deep draft, except at high tide, so cargo often had to be off-loaded to small boats capable of entering the harbour and reaching the quays. Similarly, passengers from Britain who were in a hurry were transferred here to waiting shuttle boats. Other passengers would have to wait up to six hours for high tide. This pool was located approximately 3 miles out from the docks, on a line between Whitehouse and Holywood.
Garmoyle is certainly of Irish origin but the exact derivation and meaning is uncertain. Ir. Car Maoile, 'the turn or angle of the sea inlet', is proposed at placenamesNI.org. This can be compared with Curmweela / Cor Maoile near Foynes, Co. Limerick, on the Shannon Estuary. See this name at logainm.ie
One of the last maps to mark Garmoyle was John Grantham's 1820 map of Belfast port. The pool disappeared as a result of the works carried out in the 1840s to straighten and deepen the channel. Three new lighthouses were built along the channel around 1851, the outermost of which had a green light and was known as the Garmoyle Light. It was removed in 1891.
Is it a coincidence that Garmoyle Street was named just a few years before the pool itself disappeared, or was the intention to commemorate the doomed feature?