 Walker was in almost constant attendance on King Charles I during the Civil War as Clerk Extraordinary of the Privy Council, Secretary to the Council of War, Receiver General of the King's Moneys and Secretary for War.In 1635, Walker was made Blanch Lyon Pursuivant Extraordinary, in 1637 Rouge Croix Pursuivant of Arms in Ordinary, in 1638 Chester Herald of Arms in Ordinary, in 1644 Norroy King of Arms, and in 1645 Garter Principal King of Arms, so that within less than eight years of entering the College of Arms he had attained the highest post.His appointment as Garter followed shortly on his appointment as Secretary for War and Clerk Extraordinary of the Council, so that it is plain that Charles I thought highly of his abilities.