Ms Sturgeon said they had to act “quickly and decisively ” while Scotland was “four weeks behind London”.
Describing the situation as “extremely serious”, she added: “I can confirm now…that we decided to introduce from tomorrow, for the duration of January, a legal requirement to stay at home except for essential purposes. This is similar to the lockdown of March last year.”
It comes as Holyrood was recalled to discuss further measures due to a rapid increase in Covid cases and the new highly transmissible strain.
Ms Sturgeon also announced she would keep schools closed until February 1, except for vulnerable children and those whose parents are key workers.
She admitted that she knew the decisions would not be “welcome” and that they had not been taken lightly.
The SNP leader said the measures were “devastating” and that lockdown would remain in place only if “absolutely necessary”.
The whole of mainland Scotland is already under the toughest Tier 4 restrictions, but Ms Sturgeon said this may not be enough to tackle the virus.
She also said the new lockdown may have to last longer than planned, adding: “Nothing about this is easy.”
The decision to lockdown was taken after a meeting of the Scottish Cabinet on Monday morning.