William Lowndes (1652 – 1724) was a British Whig politician who sat in the English and British House of Commons from 1695 to 1724. He was Secretary to the Treasury of Great Britain under King William III and Queen Anne. He was also secretly a member of the Assassin Brotherhood, working alongside Omar Khaled during the 17th century.
During the Great Recoinage of 1696, Lowndes was tasked by King William to contact warden of the Royal Mint, Isaac Newton, for help. Lowndes in turn sought Omar's help to do so.