On 8 July 1835 she married William King, 8th Baron King, becoming Baroness King. Their residence was a large estate at Ockham Park, in Ockham, Surrey, along with another estate on Loch Torridon and a home in London. They spent their honeymoon at Worthy Manor in Ashley Combe near Porlock Weir, Somerset. The Manor had been built as a hunting lodge in 1799 and was improved by King in preparation for their honeymoon. It later became their summer retreat and was further improved during this time. The house was built on a small plateau in woodland overlooking the Bristol Channel and surrounded by terraced gardens in the Italian style.
They had three children; Byron born 12 May 1836, Anne Isabella (called Annabella, later Lady Anne Blunt) born 22 September 1837 and Ralph Gordon born 2 July 1839. Immediately after the birth of Annabella, Lady King experienced "a tedious and suffering illness, which took months to cure". In 1838, her husband was created Earl of Lovelace. Thus, she was styled "The Right Honourable the Countess of Lovelace" for most of her married life. In 1843-4, William Benjamin Carpenter was assigned by Anabella to teach Ada’s children, as well as to act as a ‘moral’ instructor for Ada. He quickly fell for her and encouraged her to express any frustrated ‘affections’, claiming that his marriage would mean he’d never act in an “unbecoming” manner; when it became clear that Carpenter was trying to start an affair, Ada cut it off.
Ada Lovelace died at the age of thirty-six, on 27 November 1852, from uterine cancer probably exacerbated by bloodletting by her physicians.
Contact was lost with her husband after she confessed something to him on 30 August, causing him to abandon her bedside; what she told him is not known but has been theorised as a confession of adultery.