Grimston was among the secluded members who re-entered the restored Rump Parliament in February 1660, was then a member of the council of state. He was chosen Speaker of the House of Commons in the Convention Parliament of 1660. As Speaker he visited Charles II at Breda, and addressed him in very flattering terms on his return to London; but he refused to accede to the King's demand that he should dismiss Burnet from his position as chaplain to the Master of the Rolls, and in parliament he strongly denounced any relaxation of the laws against papists.