Sir Ivan Rogers has quit the civil service with immediate effect, days after resigning from his role as UK ambassador to the European Union.
The Foreign Office confirmed that Sir Ivan had not sought any further civil service job.
Sir Ivan shocked Westminster and Brussels with his resignation as permanent representative on January 3 and used an email to staff to criticise "muddled thinking" over Brexit.
A Foreign Office spokeswoman said: "Sir Ivan Rogers resigned as UK Permanent Representative to Brussels on 3 January.
"He did not seek any further civil service appointment and has therefore resigned from the civil service with immediate effect.
"We are grateful for Sir Ivan's work in Brussels and across a number of other senior positions in the civil service."