Jermyn’s ancestors held land in Rushbrooke by 1286, and acquired the manor in the second half of the fifteenth century.
Jermyn was returned for Andover in 1604 on the interest of the 3rd earl of Southampton, with whom he had served in the Irish wars.
Jermyn was elected for Suffolk in 1614, perhaps as a compliment to his dying father. The funeral was held on Easter Saturday, whereby Jermyn avoided missing any days of Parliament business.
Bury St. Edmunds, three-and-a-half miles from Rushbrooke, obtained a charter in 1614 that enfranchised the borough, giving Jermyn an opportunity to exercise electoral patronage. At the next general election he claimed seats for himself and Hay’s secretary, John Woodford, and he sat for the borough himself for the rest of his parliamentary career. In the 1621 Parliament his first appointment was to help manage the conference of 16 Feb. on the petition against recusancy.
On 12 May Jermyn praised the arms bill, to which he suggested only one alteration, that deputy lieutenants should decide on calibre, not the muster-master.
In the second sitting he urged the House on 28 Nov. to vote supply to ‘keep Count Mansfeld’s forces and ours in the Palatinate together, and not to consider the maintenance of a long war’. Clearly believing that this ‘noble action’ was worth whatever it might cost, he thought they should ‘give in such a manner as may secure the end for which it is given’.
At the next general election Jermyn was re-elected, despite a challenge from Sir Francis Cottington*, who was recommended to Bury by Prince Charles’s Council.
In the debate of 11 Mar. on supply for the war he compared a general offer to ‘the philosopher’s stone which would multiply in infinitum’, and urged the Commons to fall to particulars.
No firm resolution on supply for the war had been reached before the Easter recess, and on 10 Apr. Jermyn warned that ‘there is great preparation by the king of Spain, and a great fleet ready for the seas’.
On the opening day of the first Caroline Parliament Jermyn proposed asking the Lords to join in an address for a general fast (21 June 1625).
In the next Parliament, on 10 Feb. 1626, Jermyn moved that the committee for privileges might examine the town clerk of Bury St. Edmunds over the election of Emmanuel Giffard*, who had been returned a week after Jermyn on a separate indenture.
Such a promotion never materialized, but Jermyn continued to support the government in the 1628 Parliament. On 4 Apr. he pleaded with the Commons to put supply ahead of their grievances, warning that if ‘we fall into inconveniences, ... without great caution we are like enough to fall farther and farther’.
I protest to God, this day I came with great hope to see the wisdom of this House otherwise than now to begin to recapitulate those misfortunes that are now obvious to all; and I hoped that we should not at all have looked back, but forward.
Ibid. iv. 65.
Two days later he further admonished Eliot that attacking royal ministers was no way for Members to ‘retain themselves as far as possible within the king’s good affections’.
In the second session, at the grand committee on the customs administration on 23 Feb. 1629, Jermyn sought to discriminate between the misdeeds of officials and the king’s commands.
Jermyn was re-elected to both the Short and Long Parliaments of 1640, in which he again acted as a spokesman for the king.
