He was ordered to pay £510 in total for exceeding a 20 mile per hour limit near Lambeth Palace on 2 October last year, according to Sky News.
The 67-year-old was also handed three penalty points after being caught by a speed camera in his Volkswagen Golf on the A3036 Albert Embankment.
He was convicted in a private hearing at Lavender Hill Magistrates’ Court on Wednesday – the same day he criticised the government’s plans to combat the issue of migrants crossing the Channel on small boats as “morally unacceptable and politically impractical”.
The conviction, first reported by the Evening Standard, came just days after Welby led the King’s coronation ceremony.
Welby admitted the offence online – he was handed a £300 fine and ordered to pay a £120 victim surcharge and £90 in costs.
Sky News said the prosecution was conducted through the Single Justice Procedure, which allows the court to deal with the matter through written evidence in a private hearing.
A Lambeth Palace spokeswoman said the archbishop was aware of the speeding offence but had not been notified that it had gone to court.
“He has tried to resolve this and pay the fine three times,” the spokesperson said.
“He has all the paperwork to prove that he has tried to pay. Admin errors seem to be causing problems.”