John Buchanan, a sergeant at Police Scotland, was given the job after conducting a review of the SNP leader's safety.
Buchanan, an officer with experience of firearms incidents, was seconded by the police to the Government earlier this year to review arrangements in Bute House and the First Minister's home in Aberdeenshire.
It is also believed to have touched on security protocol when Mr Salmond is on walkabout.
Following the review, Buchanan is now based in the First Minister's private office as a "security liaison officer".
His job is to scope out potential threats and plan for events attended by Mr Salmond, such as deciding on the best entrance for the First Minister to use. He was also part of the Government entourage that visited China in November.
However, a police spokesman said the role did not amount to a bodyguard.
It is believed Mr Salmond's high profile, as well as the prominence of the independence referendum, triggered the security rethink.
Labour chief whip Macdonald said: "Alex Salmond's approval ratings may be going down, but his opinion of his own importance only ever goes up."
A Police spokesman said: "Following a review of security surrounding the First Minister for Scotland, a security liaison officer from Police Scotland has been seconded to the office of the First Minister. The role of this officer is to provide advice and guidance on physical and protective security measures, including visits and events, in relation to the First Minister."
A Scottish Government spokesman said: "We do not comment on security issues."