After serving as secretary to several more commissions, he was made Permanent Secretary to the Lord Chancellor's Office in 1915. Schuster served in this position for 29 years under ten different Lord Chancellors, and with the contacts obtained thanks to his long tenure and his work outside the Office he became "one of the most influential Permanent Secretaries of the 20th century". His influence over decisions within the Lord Chancellor's Office and greater Civil Service led to criticism and suspicions that he was a "power behind the throne", which culminated in a verbal attack by the Lord Chief Justice Lord Hewart in 1934 during a session of the House of Lords. Schuster retired in 1944 and was elevated to the peerage. Despite being officially retired he continued to work in government circles, such as with the Allied Commission for Austria and by using his seat in the House of Lords as a way to directly criticise legislation.