British astronomer and politician.

Molyneux received his B.A. (1708) and M.A. (1710) from Trinity College, Dublin. He was elected to the Royal Society in 1712. Besides pursuing a career as an astronomer, he was also active in politics, as a member of both the English parliament (1715, 1726, 1727) and the Irish parliament (1727) and as a lord of the Admiralty (1727–28).

Molyneux collaborated (1723–25) with James Bradley (Bradley, James) to improve the construction of reflecting telescopes. Molyneux worked further with Bradley in 1725, setting up a zenith-pointing telescope to try to observe stellar parallax (apparent displacement by which the distances of stars can be calculated). Although they were unsuccessful in this effort, Bradley later used the same method to discover the aberration of starlight.