With five brothers and seven sisters, St. John could expect little patrimony but considerable patronage. His first marriage brought him three messuages in Bedford, but these were promptly sold, and it was on his family’s interest that he was returned for the borough in 1614.
During the 1620s St. John’s eldest brother, Oliver St. John I*, having succeeded his father as 4th Baron St. John, proved an ambitious parliamentary patron, returning his close relatives and clients for both county and borough seats throughout the decade. Never prominent in the Commons, Sir Alexander was named to a handful of committees during the 1621 session. At a committee of the whole House on religion on 5 Feb., he was one of those delegated to draft a petition to the king ‘for the execution of the laws against Jesuits, seminary priests and recusants, and for avoiding danger by them and suppressing their insolency’. Five weeks later, he was one of those appointed to confer with the Lords about the best course to take against monopolists following the king’s qualified approval of the investigations thus far (12 March). He was subsequently named to the committee appointed to draft the grievances to be submitted to the king before the summer recess (16 May).
From 1624 Sir Alexander was joined in the Commons by his elder brother Sir Anthony. The records do not often distinguish between the two men, although it seems likely that Sir Alexander was generally the man cited as ‘Sir A. St. John’; on this basis, and that of his earlier parliamentary experience, he was clearly the man appointed to the privileges’ committee in 1624, 1625 and 1626.
In 1623 St. John’s sister married the 4th earl of Bath, and he quickly joined her in Devon, managing the Tawstock estate. Bath had sufficient influence with his cousin Sir Francis Russell* to procure St. John a seat on the county bench, the colonelcy of the north Devon militia, and appointment as a deputy lieutenant. In 1626 Sir Alexander relinquished his seat at Bedford to his brother Sir Beauchamp, and was elected for Barnstaple, two miles from Tawstock, on Bath’s interest. He was among those named to attend the joint conference of 7 Mar., at which Archbishop Abbot and the earl of Pembroke outlined plans for a renewed offensive against Spain. However, he wisely stayed clear of any involvement in the main agenda of the session, the impeachment of the duke of Buckingham: most of his committee nominations concerned uncontroversial private bills.
In September 1628 St. John fell out with Bath’s heir-presumptive, Sir Henry Bourchier, over the withholding of the latter’s annuity; this eventually led Bourchier to challenge the earl to a duel, which matter St. John referred to the Privy Council.
