At the Restoration (1660) Newcastle returned to England, and succeeded in regaining the greater part of his estates, though burdened with debts, his wife estimating his total losses in the war at the enormous sum of £941,303. He was reinstated in the offices he had filled under Charles I and appointed a Gentleman of the Bedchamber. He was invested in 1661 with the Order of the Garter which had been bestowed upon him in 1650, and was advanced to a dukedom (of Newcastle-on-Tyne) on 16 March 1665.

He retired, however, from public life and occupied himself with his estate and with his favourite pursuit of training horses. He established a racecourse near Welbeck. In his later years, he suffered from Parkinson's disease, and the sudden death of his second wife was a blow from which he never recovered. With John Dryden's assistance he translated Molière's L'Etourdi as Sir Martin Mar-all (1688). He contributed scenes to his wife's plays, and poems of his composition are to be found among her works.

Cavendish was the patron of, among others, Jonson, Shirley, Davenant, Dryden, Shadwell and Flecknoe, and of Hobbes, Gassendi and Descartes. During their stay in Antwerp, the Cavendishes had a music chapel of 5 musicians. They were acquainted with several of the contemporary English composers, and Newcastle's library contained a substantial collection of music of these composers.

The department of Manuscripts and Special Collections, The University of Nottingham holds a number of papers relating to the 1st Duke: the Cavendish Papers (Pw 1), part of the Portland (Welbeck) Collection, includes some of his personal papers; the Portland Literary Collection (Pw V), also part of the Portland (Welbeck) Collection, contains many of his literary papers; and the Newcastle (Clumber) Collection (Ne) includes some estate papers from the time of the 1st Duke, for example, relating to his purchase of Nottingham Castle.