While practising in London he made the acquaintance of many of the noted men of the time, both physicians and theologians, and came much into contact with the Cambridge latitudinarians at the house of his kinsman, Thomas Firmin.
In 1670 he attended Arthur Capell, 1st Earl of Essex in his embassy to Denmark, and in 1672 was in France with the Dowager Duchess of Northumberland.
He retained his professorship at Gresham College till 10 October 1679, when he retired from medical practice and prepared himself for ordination.
Mapletoft was an original member of the Company of Adventurers to the Bahamas (4 September 1672), but, being abroad at the time, transferred his share to Locke.
In the same year he was using his influence and purse in support of Isaac Barrow's scheme for building a library at Trinity College.
He was elected a fellow of the Royal Society on 10 February 1676, was member of council in 1677, 1679, 1690, and 1692, and as long as he practised the medical profession took part in the discussions and experiments.
He was an original member and active supporter of the Society for the Propagation of the Gospel in Foreign Parts (incorporated by charter in 1701), a benefactor to the library and buildings of Sion College, of which he was president in 1707, and one of the commissioners of Greenwich Hospital.
He died in Westminster on 10 November 1721, in the ninety-first year of his age, and was buried in the chancel of the church of St. Lawrence Jewry.
Mapletoft's published works, apart from single sermons, include: The last two are selections from Greek authors with Latin translations, and were reprinted in 1731.
to John Ward's 'Lives' (p. 120) are printed three Latin lectures by Mapletoft on the origin of the art of medicine and the history of its invention, under the title Praelectiones in Collegio Greshamensi, Anno Dom.
1707), advocate of Doctors' Commons (12 July 1707), and commissary of Huntingdon; died on 3 December 1716, and was buried in St. Edward's Church, Cambridge.