William Fitzwilliam, 2nd Baron Fitzwilliam (c.1609 – 21 February 1658) was an English nobleman and politician who sat in the House of Commons of England between 1640 and 1653.
Fitzwilliam was the son of William Fitzwilliam, 1st Baron Fitzwilliam and his wife Catherine Hyde.
In April 1640, Fitzwilliam was elected Member of Parliament for Peterborough in the Short Parliament. He was re-elected in November 1640 for the Long Parliament where he remained throughout its duration. Fitzwilliam inherited the peerage on the death of his father in 1643.
Fitzwilliam died at the age of 49.
Fitzwilliam married Jane Perry, daughter of Hugh Perry and his wife Catherine Fenn in 1638. Their son William succeeded to the title and was later created Earl Fitzwilliam. Their daughter Jane married Sir Christopher Wren.