[2][3][6] His doctoral supervisor was Professor Peter Hennessy, and his thesis was entitled The Joint Intelligence Committee and the German Question, 1947–61.

[10] On 8 January 2016, Case was announced as the next Principal Private Secretary to the Prime Minister in succession to Chris Martin who had died while in office.

[2][10] In March 2017, Case was announced as the Director General for the UK–EU Partnership, being succeeded by Peter Hill as Principal Private Secretary to the Prime Minister on 10 May 2017.

[11] On 23 June 2017, he was appointed a Commander of the Royal Victorian Order (CVO) in recognition of his service as Principal Private Secretary to the Prime Minister.

[15] In March 2018, it was announced that Case would be the next Private Secretary to Prince William, Duke of Cambridge; he took up the appointment in July 2018.

[24] In December 2021, the Prime Minister appointed Case to lead an inquiry into the Westminster Christmas parties controversy, where government departments had been alleged to have carried out social gatherings in late 2020 in contravention of COVID-19 regulations.

"We must consider how we can streamline our workforce and equip ourselves with the skills we need to be an even more effective, lean and innovative service that continues to deliver for the people we serve," he wrote.

[31] In September 2024 he was under pressure to bring forward his departure date, amid anger over a series of damaging leaks and briefings.

[34] In evidence from the Commons privileges committee, which found that the former prime minister deliberately misled MPs over lockdown gatherings, Case denied giving Boris Johnson any reassurances that Covid rules and guidance were followed at all times.

Case, who was said to be in discussion with the then-Health Secretary Matt Hancock, reportedly mocked holidaymakers stuck in hotel rooms by the UK's quarantine policy, saying it was "hilarious" and how he wanted to "see some of the faces of people coming out of first class and into a Premier Inn shoe box".

[37] Case described Johnson as "nationally distrusted figure" and warned the public were unlikely to follow isolation rules laid down by him.