Middleton’s family rose to prosperity in the Wealden iron trade, although his great-grandfather was a Crown servant in the reign of Henry VIII. By the late 1580s he was a partner in his uncle’s gunfounding business, which he subsequently inherited. The firm’s profits do not seem to have been adversely affected by peace with Spain, when they probably switched to the export trade.
In 1614 Middleton was returned for Horsham, presumably on his own interest, and was subsequently re-elected to every Parliament in his lifetime. It is difficult to distinguish him from Robert and Hugh Myddelton in the surviving records of the Addled Parliament. However, as the clerk felt the need to specifically identify Middleton as ‘John Middleton’ when he was appointed to the committee to consider the bill against the export of artillery on 11 May it is likely that the references to ‘Mr. Middleton’ in the records relate to one of the other Members.
Although Hugh Myddelton also sat in the third Jacobean Parliament, it was presumably Middelton who was among those appointed to the drafting committee for another artillery export bill on 26 Mar. 1621 and to the committee after its second reading on 14 May. He was also probably the Member appointed to the committee for the bill to establish a new trust for the Sussex Catholic Viscount Montagu (16 March).
In the first Caroline Parliament Middleton was appointed to consider a bill ‘for increase of timber and wood’ (8 July), a matter of interest to him as the iron industry relied on plentiful supplies of timber. Indeed, he and his partners had used £4,200 worth of wood from one Sussex park alone between 1589 and 1596.
By 1620 Middleton owed Smith some £4,000, possibly arising from his involvement in the financial affairs of the spendthrift Thomas Shelley*, whose sister had married Middleton’s eldest son in 1610.
In 1627 Middleton was forced to seek Crown protection from the creditors he had acquired ‘by suretyship for Mr. Shelley’, assuring the Privy Council that he could, given time, pay off all debts, ‘and yet leave a moderate fortune for himself and his children’.
