Pc Luke Wilson, 28, was previously found guilty of assaulting Johnny White while out for drinks with fellow officers at a Be At One bar in King William Street, in the City of London, last July.
Westminster Magistrates’ Court heard that Wilson, who is based in Lewisham, was breaking Covid rules at the time, as he and other members of the group moved between tables around the venue.
Wilson said he and the others were police officers when asked by Mr White, and when the victim challenged the group, Wilson head-butted him.
The court was told the assault left the Mr White with “reddening” of the skin which had subsided by the following day.
Wilson still claims his innocence but was remorseful for breaching Covid rules, the court heard.
District Judge Briony Clarke on Tuesday passed a sentence of 10 weeks in prison, suspended for 12 months.
She also ordered Wilson, of Gravesend, Kent, to carry out 80 hours of unpaid work and pay £200 in compensation to the victim, as well as £775 in court costs and a £128 victim surcharge.
Passing sentence, she said anyone who saw CCTV footage of the incident, played during the trial, would have been “shocked”.
Tom Bushnell, representing Wilson, told the court the assault was “out of character” and a “moment of madness”, adding that it “pales” in comparison with his “brilliant career” as a police officer.
The Metropolitan Police said Wilson had remained on restricted duties since his conviction and misconduct proceedings would take place as soon as possible.
Chief Superintendent Trevor Lawry, in charge of policing for Lewisham, Bexley and Greenwich, said: “Whether on or off duty, police officers are expected to uphold the high standards we expect as an organisation.
“However, Pc Wilson’s behaviour fell far below this and it is right that following a police investigation he has had to face up to his actions in court.”