In 1549 he was, with eight other advocates, chosen by the Court of Session to plead before them in all cases.
[1] When John Knox, on account of his letter about the mass, was in 1563 accused of treason, Spens came to him privately, and expressed the opinion that Knox had not been guilty of anything punishable by law.
Knox stated that when Spens was commanded to accuse him before the queen, he did so, but "very gently".
He adhered to the queen's party after her marriage to Henry Darnley; and he was officially entrusted with the prosecution of the murderers of David Rizzio.
He also attended officially at the indictment of James Hepburn, 4th Earl of Bothwell for the murder of Darnley.