William de Ros, 3rd Baron de Ros (died February 16, 1342) was the son of William de Ros, 2nd Baron de Ros.

As 3rd Baron de Ros of Hamlake, Werke, Trusbut & Belvoir, he was summoned to Parliament during the reigns of Edward II and Edward III of England. In 1321 he completed the religious foundation which his father had begun at Blakeney. He was created Lord Ross of Werke. He was appointed Lord High Admiral and was one of the commissioners with the Archbishop of York, and others, to negotiate peace between the king and Robert de Bruce, who had assumed the title of king of Scotland.

He married Margery De Badlesmere (1306-1366), the eldest sister and co-heir of Giles, Baron Badlesmere of Leeds Castle, county of Kent. She survived her husband by many years and was one of the very few English people present at the Jubilee, at Rome, in 1350; the king had tried to prevent the attendance of his subjects at this ceremony on account of the large sums of money usually taken out of the kingdom on such occasions. Their children were:
• William de Ros, 4th Baron de Ros
• Thomas de Ros, 5th Baron de Ros
• Sir John De Ros
• Margaret de Ros
• Matilda de Ros

William de Ros was buried at Kirkham Priory, near the great altar.