In 1651 he was assigned by the court as one of the counsel for Christopher Love on his trial for high treason in plotting with the Scots to bring about the restoration of the monarchy; but exception was taken to Archer on the ground that he had not subscribed the engagement to be true to the commonwealth, as required by a resolution of the House of Commons passed on 11 October 1649, to be subscribed by public functionaries 'and by' all sergeants at law, counsellors, officers, ministers, and clerks, and all attorneys and solicitors.'
On 27 November 1658 he was made a Serjeant, the appointment being confirmed by Charles II on 1 June 1660; but his elevation to the bench, which had occurred in the interim (15 May 1659), was thereby tacitly annulled.
Archer is characterised by Roger North as one 'of whose abilities time hath kept no record unless in the sinister way,' as uncertain in his law and afraid of a long and intricate cause.
He appears, however, to have held decided and sound opinions on the construction of his own patent; for when the king in the winter of 1661 attempted to remove him from his office he stood stoutly upon his right to hold it on the terms of the patent, 'quamdiu se bene gesserit,' and refused to surrender the patent without a writ of scire facias, the proper legal mode of procedure to annul a royal grant; but which was so little to the taste of the king that Archer continued, until his death, legally justice of the common bench, and in receipt of his salary as such, though relieved by royal prohibition from the performance of the duties of the office, which were discharged by Sir William Ellis.
He later married Eleanor (Curzon), daughter to Sir John Curson, Baronet of Kedleston, Derbyshire, by whom he had one child, John, who died without issue, 7 November 1706, having by his will left the Coopersale estate in Essex to William Eyre of Gray's Inn, on condition that he married Eleanora Wrottesley (a niece of the testator), daughter to Sir Walter Wrottesley, 3rd Baronet, and assumed the name of Archer, which happened in due course.