Gostwick was knighted on 24 November 1668, before succeeding to his father's baronetcy on 24 February 1671. He was appointed Burgess of Bedfordshire in 1676. In 1679, he was appointed
High Sheriff of Bedfordshire, serving until 1680. His grandfather had previously held the post from 1626 to 1627 as well as his great-grandfather,
Sir William Gostwick, 1st Baronet, who held the post from 1595 to 1596. Although he was still purchasing land as late as 1686, when he added another Bedfordshire manor to his estate, he began borrowing money the following year and, by the time he stood for Parliament in 1698, had already taken out mortgages of over £10,000 on his property. His last recorded vote was on 18 June 1713, over the French commerce bill, which he opposed. He did not stand again, likely because he was crippled by debt. Around 1717, "he agreed to sell his entire estate for £47,000, some £9,000 less than the total of his debts, in the hope that his creditors would agree to take a loss and divide the purchase price among themselves, the encumbrances being 'so confused and intermixed, and the priorities unknown and so difficult to be discovered'. The scheme fell through, however, because of the refusal of a few creditors to accede, including the biggest, the
Duke of Marlborough," who had acquired about "£27,000-worth of the mortgages on Gostwick's estate." ==Personal life==