Paul Murphy will be replaced as Northern Ireland Secretary by Peter Hain as part of British Prime Minister Tony Blair's cabinet reshuffle.
Mr Blair reappointed finance minister Gordon Brown and Foreign Secretary Jack Straw today but changed a host of other ministers after winning a third straight election.
Geoff Hoon will leave the defence ministry, replaced by Health Secretary John Reid, officials said. In turn, Reid's job will be filled by Trade Secretary Patricia Hewitt.
Mr Hoon, criticised over the deaths of British soldiers in Iraq, would become the government's leader in parliament.
In what was probably the crucial move of Britain's election campaign, Mr Blair promised Mr Brown he would remain as Chancellor of the Exchequer, acknowledging his popularity in the Labour Party and with the public.
"The prime minister's view is that this reshuffle puts key reformers in key public service departments and represents the Chancellor and the prime minister working closely together," Mr Blair's spokesman told reporters.
Home Secretary Charles Clarke and Education Secretary Ruth Kelly were to remain in their posts, having been appointed only a few months ago. Mr Straw had been thought to be vulnerable but was untouched.
He helped persuade Mr Blair to promise a referendum on the European Union's constitution next year, a vote that looks tough to win given Britain's eurosceptic public.
If Mr Blair fails to persuade the public to back the constitution, it could fatally undermine his grip on power.
To that end, the prime minister promoted rising star Douglas Alexander to Minister for Europe, a position that was given greater influence by being attached to the cabinet of top ministers for the first time.
David Blunkett made an early return as Work and Pensions Secretary having resigned as Home Secretary last year after an inquiry discovered that his department aided a visa application by his ex-lover's nanny.
Alan Johnson, who had that job before the election, took a new cabinet post, Productivity, Energy and Industry.