"[citation needed] With such claims it is not surprising that he was included in the first batch of new Serjeants called by Charles II on 4 July 1660, to take the degree on the following Michaelmas; and was immediately engaged on the part of the crown to advise with the judges relative to the proceedings to be adopted against the regicides.

On 8 November, he was made king's Serjeant, and in that character was one of the counsel on the trial of Sir Harry Vane, towards whom his conduct was unfeelingly harsh and insulting.

The dissatisfaction with the verdict which he is represented to have expressed seems to proceed, not from his disbelief in the existence of witchcraft, but from his opinion that the evidence was not sufficient to convict them.

Within two years after his promotion, the death of Sir Robert Hyde made a vacancy in the office of chief justice of the King's Bench.

He presided over the trial of an innocent but insane Frenchman, Robert Hubert, who confessed to setting the fire in the King's Bakehouse in Pudding Lane.

Kelynge later led a commission to examine numerous other witnesses and concluded that the fire was started by accident and was so calamitous because of a number of circumstances, including the very strong easterly wind.

In 1667 numerous complaints and impeachment recommendations were made against him in parliament by the opposition, the "gentlemen of the county" for divers "high proceedings" in the execution of his office, such as fining of juries for bringing in verdicts contrary to the evidence, and for referring to Magna Carta as "Magna Farta" (this seems to have been a common gibe, even among judges, at the time); for which he was obliged to answer before the House of Commons.