James Ley, 1st Earl of Marlborough (c. 1552–1629) was an English judge and politician who sat in the House of Commons at various times between 1597 and 1622.

That November he became a serjeant-at-law and in December James I knighted him: the King formed a high opinion of his abilities.

Ley was called back to England in 1608, ostensibly to brief the English Privy Council on the settlement of Ulster.

The same year he married his third wife Jane Boteler, niece of the prime royal favourite Buckingham.

Late in 1624, through the influence of Buckingham, Ley replaced Cranfield as Lord High Treasurer, also being sworn as a Privy Councillor.

His treasurership was hampered by Charles I's financial difficulties, and his own lack of experience in the world of finance.

None of his works on legal or antiquarian subjects were published in his lifetime, but his grandson James Ley, 3rd Earl of Marlborough arranged for the publication of his treatise on wardship in 1642, and a collection of law reports in 1659.

Four of his papers to the Society of Antiquaries were published by Thomas Hearne in his Collection of Curious Discourses (1720).