The fact his sacking comes as an even bigger surprise suggests he was doing a good job at Dover House, Whitehall headquarters of the Scotland Office, in his own quiet, efficient way.
The former accountant's qualities - he's thoughtful, reasonable and unflappably calm - were ideally suited to the task in hand in 2010: steering the complicated Scotland Bill through the Commons.
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The Liberal Democrat Berwickshire, Roxburgh and Selkirk MP's diplomatic demeanour also served him well in negotiations leading to the Edinburgh Agreement, the deal between the UK and Scottish governments which paved the way for the referendum.
However the feeling in the UK Government now is that a more combative figure is required to see the referendum campaign through to its conclusion.
Enter Alistair Carmichael, MP for the other end of Scotland, Orkney and Shetland.
A lawyer by profession, he was tipped for the cabinet job in 2010, having served as Shadow Secretary of State for Scotland in the run-up to that year's election. His experience then, taking on the likes of Nicola Sturgeon in televised debates, has now helped him land the job. Within his party he is admired as a strong debater and campaigner, able to mix forensic analysis with humour, and Deputy Prime Minister Nick Clegg is hoping he will use those skills to the full to take the fight to the Scottish Government in the months ahead.
Mr Moore went head-to-head with Nicola Sturgeon in an STV debate in May, the first major televised clash of the campaign, and was generally thought to have come off second best. Mr Carmichael, say Lib Dem colleagues, "brings a different style" - a more confrontational one, to be specific.
Both men were told the news by the Deputy Prime Minister on Friday. Mr Moore, understandably, is said to be disappointed at not having the chance to see the referendum campaign through to the end, but the way has been left open for him to re-enter government at a future date. Mr Carmichael, say colleagues, is relishing the challenge.