The Department for Exiting the European Union (DExEU) will be "wound up" on the day the UK leaves the EU, the government has announced.
On January 31 the government plans to shut the department, fronted by Brexit Secretary Steven Barclay, and several staff members are expected to be out of a job.
A government spokesperson thanked all outgoing staff "for all their work" and said they will receive help finding new jobs.
Established in 2016 following the Brexit referendum, the department is responsible for overseeing negotiations to leave the EU and establish the future relationship between the bloc and Britain.
But Boris Johnson has vowed to take Britain out of the bloc at the end of next month, and will begin driving the necessary legislation through Parliament from Friday.
The government's decision to shut the department indicates senior figures believe it will be redundant following the UK's departure from the EU.
But critics have said there will be lots more work to do on Brexit during the transition period, which is scheduled to run until the end of 2020.
Winding down the department follows reports that the PM is planning a major shake-up of Whitehall - with suggestions that the best DExEU staff may join the Cabinet Office to boost numbers in Britain's EU negotiating team.
Other ideas floated include splitting energy and climate change from the business department again and merging the Department for International Trade with the business department.
The Foreign Office and the Department for International Development could also be aligned to shift the aid budget's focus and ensure it aligns with foreign policy goals.