The Government department was set up under David Davis to steer the UK through the process of leaving the European Union.
But the TaxPayers’ Alliance, which carried out the research, urged ministers to make sure all employees were worth their high salaries.
Chloe Westley, campaign manager at the organisation, said: “When colleagues across the public sector are facing a pay freeze and taxpayers up and down the country are struggling to pay their bills, these high salaries may raise eyebrows.
“However, we recognise it’s imperative to have the brightest minds in the country working towards our exit from the EU. The important thing is that the department ensures that all those on high salaries are indeed worthy of them.”
The Department now has more than 450 employees, of which more than 350 staff are on loan from across the civil service.
The information was released in its official accounts and a series of written answers to Labour MP John Trickett.
The Brexit department said it was “continuing to recruit the brightest and the best from across the civil service, the wider public sector and private sector.
“Numbers are regularly changing and our aim is to have a streamlined department, while hiring in the right skills and experience to get the best outcome for the UK”.
Overall the department spent £24million, including £1.2million on IT.