John Bird (1709– 31 March 1776) was a British mathematical instrument maker who was notable for inventing the sextant.

Bird was commissioned to make a brass quadrant 8 feet across for the Royal Observatory at Greenwich, where it was mounted on 16 February 1750, and where it is still preserved.

[2][3] Bird supplied the astronomer James Bradley with further instruments of such quality that the commissioners of longitude paid him £500 (a huge sum) on condition that he take on an apprentice for 7 years and produce in writing upon oath, a full account of his working methods.

When the Houses of Parliament burned down in 1834, the standard yards of 1758 and 1760, both constructed by Bird, were destroyed.

Bird, with his fellow County Durham savant William Emerson, makes an appearance in Mason & Dixon, the acclaimed novel by Thomas Pynchon.