Liberal Democrat MP Danny Alexander will serve as Scottish secretary in the new Tory/Lib Dem coalition government.
The appointment of the Inverness, Nairn, Badenoch and Strathspey MP came even though his party's policy has been to scrap the Scotland Office.
Meanwhile, SNP ministers have claimed UK government spending cuts could take £600m out of the Scottish budget.
The new prime minister, David Cameron, is preparing to visit Scotland within the next few days.
The new UK government will look at implementing the recommendations of the Calman Commission review of devolution to give Holyrood far greater tax varying powers.
And there are plans to stop children being detained at the Dungavel Immigration Removal Centre, in South Lanarkshire, where, in some cases, babies and young children have been held for more than a year.
There will also be a commission on a possible English Assembly and to look at the West Lothian question - whether it is right for Scottish MPs to vote on policies which affect other parts of the UK.
Mr Alexander, 37, who played a key role for the Lib Dems during their campaign and post-election coalition talks with the Tories, will play an important role in relations between the UK and Scottish governments. He is seen as a rising star within the Liberal Democrats.
He told BBC Reporting Scotland his approach would be "about ensuring the UK government can also work together with the Scottish government and the Scottish Parliament".
Mr Alexander said: "My first act as Scottish Secretary was to phone Alex Salmond, the first minister, to have a conversation with him, which was a very friendly conversation, to say that what we want to do is to try to work together in the spirit of co-operation.
"We've got a programme for government which we've set out which I think will deliver enormous benefits to the people of Scotland."
David Mundell, the sole Scottish Tory MP, lost out on the top Scotland Office job after being shadow Scottish secretary for the past three years, but will serve as Mr Alexander's junior minister of state.
Andrew Black Political reporter, BBC Scotland news website
Danny Alexander may only have become an MP in the last parliament, but has risen quickly in the party.
After holding several frontbench roles, he became leader Nick Clegg's chief of staff, before taking charge of the party's general election manifesto.
He rose to wider public attention as a key member of the Lib Dem negotiating team sent in to hammer out a power-sharing deal with the Tories.
Educated in Fort William and Oxford, the 37-year-old married dad joined the Scottish Liberal Democrats as a press officer in 1993 and later ousted Labour to become MP for the newly redrawn Inverness, Nairn, Badenoch and Strathspey, seat in 2005.
He was also the former media chief of pro-euro campaign group Britain in Europe, which brought together leading Labour and Lib Dem voices with business groups.
As Scottish secretary, rather than Scotland's sole Tory MP David Mundell, Mr Alexander instantly has several big issues in his in-tray.
As well as playing a key role in relations between the UK and Scottish governments, top of the list is enhanced powers for the Scottish Parliament, as put forward by the Calman Commission devolution review, and then there's the thorny issue of any UK government spending cuts which might hit Scotland.
And next year's Scottish Parliament elections, where the Lib Dems will go head-to-head with the Tories in the fight for votes, could pose some political problems for the new secretary of state.
The SNP's Stewart Hosie, MP for Dundee East, said: "Danny Alexander will have to show great dexterity in a post he wants to see abolished."
Scottish Tory leader Annabel Goldie said the new deal was "an opportunity to show that we can be a government for the good of all of Britain".
She added: "The people of Britain wanted politicians to work together for the good of the country and David Cameron is committed to doing that.
"He is committed to repairing the broken relationship between our parliaments and our governments and he has said he will treat Scotland with respect."
Scottish Labour leader Iain Gray branded the coalition between the two parties a "deal with the devil", adding: "Labour warned that a vote for the Liberal Democrats would only help David Cameron into Downing Street, and we were right."
Meanwhile, Scottish Finance Secretary John Swinney told the Scottish Parliament's economy committee a planned £6bn cut by the new UK government had "very serious" implications for Scotland, although Labour argued he had "no inside track" on where reductions would come.
"Without being too precise about it, we're talking about a sum of money which is in the sphere of £500-£600m of consequential impact in Scotland," said Mr Swinney.
Scottish First Minister Alex Salmond, who congratulated Mr Cameron by phone, said his visit to Scotland would focus on economic recovery.
Mr Salmond reiterated his concerns in a letter to the prime minister, in which he also expressed an aspiration for the two governments to go forward on the basis of "mutual respect".
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