Maunder, who was born in London, took some courses at King's College there but did not obtain a degree. After working briefly in a bank he became photographic and spectroscopic assistant at the Royal Observatory, Greenwich, in 1873. Maunder's appointment allowed Greenwich to branch out from purely positional work, for Maunder began a careful study of the Sun, mainly of sunspots and related phenomena. After 1891 he was assisted by Annie Russell, a Cambridge-trained mathematician, who must have been one of the first women to be so employed. She became his wife in 1895.

It had been known since 1843 that the intensity of sunspot activity went through an 11-year cycle. In 1893 Maunder, while checking the cycle in the past, came across the surprising fact that between 1645 and 1715 there was virtually no sunspot activity at all. For 32 years not a single sunspot was seen on the Sun and in the whole period fewer sunspots were observed than have occurred in an average year since. He wrote papers on his discovery in 1894 and 1922 but they aroused no interest.

More sophisticated techniques developed in recent years have established that Maunder was undoubtedly correct in the detection of the so-called Maunder minimum. Also, the realization that the period of the minimum corresponds to a prolonged cold spell suggests that Maunder's discovery is no mere statistical freak. It may throw light on the Sun's part in long-term climatic change and on possible variations in the processes within the Sun that produce the sunspots.