He set a record for length of service when repeatedly elected to serve as Speaker of the House of Commons, where he was known for his integrity.

As his Post Office position was not compatible with a parliamentary seat, he passed it on to his younger brother Richard when he entered Parliament in 1720 for Guildford.

(She had married his younger brother Richard, whose life interest in her estate Arthur purchased after her death.)

During this period, he was known to have declared against a proposal to levy Roman Catholics in 1722, and opposed the motion to reverse Bolingbroke's attainder in 1725.

The following year, on 13 May 1729, he was made Chancellor and Keeper of the Great Seal to Queen Caroline, who was godmother to his son George in 1731.

While he continued to participate in ordinary political activity, speaking and voting in committee, he did not hesitate to oppose Government policy when necessary.

He insisted on rigidly observing parliamentary forms and procedure, which he viewed as a protection to independent MPs.

He died at his home in London in 1768 and was buried at Thames Ditton, but his body and that of his wife were later removed to the Onslow burial place in Merrow Church, Surrey.

Horace Walpole at one point said of him that he was "too pompous to be loved, though too ridiculous to be hated", but subsequently wrote in more considered fashion: No man had ever supported with more firmness the privileges of the House, nor sustained the dignity of his office with more authority.

His disinterested virtue supported him through all his pretensions; and though to conciliate popular favour he affected an impartiality that by turns led him to the borders of insincerity and contradiction; and though he was often so minutely attached to forms, that it made him troublesome in affairs of higher moment, it will be difficult to find a subject, whom gravity will so well become, whose knowledge will be so useful and so accurate, and whose fidelity to his trust will prove so unshaken.