He was returned to parliament for Plympton Erle in October 1679, and again for the parliaments of 1681, 1689 and 1690. He was active on various economic affairs committees, helping pass the Tobacco Act and renew the charter of the East India Company. He was made a Justice of the Peace for Devon in 1689 and an honourary trustee of the National Land Bank. His most significant appointment was as a member of the Board of Trade between 1696 until 23 April 1709. While there he participated in the recoinage debate, produced a report on the judicial system of Barbados and advocated a unified military command for the American colonies. In 1677 he served on a special commission of the East India Company, accusing the directors of monopolising the trade through jobbery and refusing to issue new stock, and also condemned the export of gold bullion, which he saw as supressing domestic production and employment. As a result he lobbied the House of Commons in 1689 to establish a new, national company, and presented written and oral testimony to the House of Lords in 1696 showing the harmful effects of importing indian-manufactured goods and exporting bullion. In response the Lords and Commons opened up the trade lanes to India, establishing a well-regulated company to manage this.
As a by-product of his public career Pollexfen published a series of political and economic essays. After Charles Davenant published his An Essay on the East India Trade in 1697, Pollexfen responded with his essay England and East India Inconsistent in their Manufactures, and also published A Discourse of Trade and Coyn, an extended version of which was republished to counter William Lowndes proposal of recoinage. In 1699 he published A Vindication of some Assertions Relating to Coin and Trade, and a year later republished of Trade. He died shortly before 15 February 1715, when he was buried at St Stephen Walbrook.