Jermyn’s education consisted primarily of foreign travel. He can scarcely have entered his teens when licensed in 1618 to tour the Continent for three years. By early 1623 he was abroad again, this time as a member of the household of the English ambassador to Spain, the earl of Bristol (John Digby*). While there, he failed to recognize his father’s patron, the duke of Buckingham, when the latter arrived unannounced in Madrid to hasten the Spanish Match negotiations. Fortunately the royal favourite was not offended, and a relieved Jermyn’s next letter home ‘abounded in the expression of his joy for the honour and favours done him’ by the duke.37 APC, 1618-19, p. 103; Harl. 1581, f. 352.
Jermyn first entered Parliament while still under age, sitting for Bodmin in 1625 and 1626 on the interest of his maternal uncle, Sir Robert Killigrew*. His youth and inexperience accounts for his failure to contribute to the Commons’ proceedings in either year.38 Vivian, Vis. Cornw. 270. By 1627 he had become a gentleman usher to the queen, and in July that year he was sent to France by Henrietta Maria to convey her condolences to Louis XIII on the death of the duchess of Orléans. As this visit coincided with Buckingham’s expedition to the Ile de Ré, Jermyn was briefly mistaken by the French for a peace envoy.39 CSP Ven. 1626-8, pp. 297-8, 310, 335. He returned to the Commons in 1628, this time representing Liverpool on the nomination of his cousin by marriage, (Sir) Humphrey May*. Either he or his brother Thomas was added on 3 June to the committee to consider a petition from the puritan printer, Michael Sparkes.40 Vis. Suff. ed. Howard, i. 295-6; CD 1628, iv. 59. During the parliamentary recess, Jermyn was seconded to Jersey to train the island’s militia, presumably on the strength of his father’s reversionary title to the governorship.41 APC, 1628-9, pp. 282, 320. It is unclear whether he returned to Westminster for the 1629 session. Either way, on 9 Feb. he was licensed with his cousin, John Poley*, to promote a treatment for sheep-rot developed by a Suffolk neighbour, Sir Robert Le Gris.42 C66/2462/37; Vis. Suff. i. 295-6; Hervey, 33.
This medical venture helped set the tone for the following decade, as Jermyn and his brother Thomas exploited their Court connections to secure a series of potentially lucrative joint grants. These included the clerkship of warrants and enrolments in Common Pleas, and the Exchequer clerkship of the Pipe. However, all these posts were held in reversion, and Jermyn apparently received no benefit from any of them until after the Restoration, when he finally became joint registrar of Chancery.43 Cal. Docquets of Ld. Kpr. Coventry ed. J. Broadway, R. Cust and S.K. Roberts (L. and I. Soc. spec. ser. xxxiv), 184, 195, 198, 203, 206, 209; T. Rymer, Foedera, ix. pt. 2, p. 205; G.E. Aylmer, King’s Servants, 97. Meanwhile, he rose steadily in favour with Henrietta Maria. In 1632 Jermyn was again sent to Paris, this time to congratulate the queen’s mother, Marie de Medici, on surviving a coach accident.44 CSP Dom. 1631-3, p. 420. In the following year he jeopardized his position by seducing one of Henrietta Maria’s maids of honour, Eleanor Villiers, and then refusing to marry her when she became pregnant. A scandalized Charles I sent him abroad to cool his heels, but he was allowed to resume his Court functions in August 1634. Less than 12 months later he was acknowledged to be one of the queen’s principal favourites, a position he never again relinquished.45 Ibid. 1633-4, p. 50; C115/105/8151, 8159, 8164; 115/106/8432; PC2/43, p. 244; Works of Abp. Laud ed. J. Bliss, vii. 145, 161, 172. Regularly selected as her personal agent overseas towards the end of the decade, his promotion in 1639 to the rank of master of the horse confirmed his now dominant standing within Henrietta Maria’s Household.46 CSP Ven. 1636-9, pp. 449, 458, 500-1, 504-5, 511, 534, 545; HMC De L’Isle and Dudley, vi. 204.
Jermyn sat for Corfe Castle in the Short Parliament, but seems not to have sought a Commons’ seat in the following autumn. His prominent role in the First Army Plot of 1641 identified him as a diehard foe of the parliamentarian leadership, and after the outbreak of the Civil War he was consistently excluded from peace negotiations. Raised to the peerage as Lord Jermyn of Bury St. Edmunds in 1643, he became the queen’s chamberlain early in the following year, and accompanied her into exile a few months later, running her household in France. Their increasingly intimate relationship during the Interregnum prompted widespread gossip that he had secretly married her after Charles I’s execution.47 C. Russell, ‘The First Army Plot of 1641’, TRHS (ser. 5), xxxviii. 89-92; CCC, 139; Clarendon, iv. 312; Diary of Samuel Pepys ed. R. Latham and W. Matthews, iii. 263. Rewarded with the earldom of St. Albans at the Restoration, Jermyn remained the queen dowager’s principal servant until her death in 1669, although Charles II also frequently employed him as ambassador to France. Simultaneously, he played a major role in the development of London’s West End, using land obtained from Henrietta Maria to create St. James’s Square and the surrounding streets, one of which still preserves his surname.48 J. Summerson, Georgian London, 41-2; Hervey, 272, 275. In his old age he served for three years as lord chamberlain, but thereafter largely retired from public life. Jermyn died at his house in St. James’s Square in January 1684. At his own request, he was buried with his ancestors at Rushbrooke. His heirs were his nephews Thomas Jermyn†, who inherited his barony, and Henry Jermyn, later Lord Dover. The fate of his illegitimate child, whom he never acknowledged, is not known.49 Hervey, 61, 248, 275; PROB 11/375, ff. 276-7.