Both the blazer and the shirt are still available to shop online.
Mrs Johnson, who is expecting her second child, finished the look with black skinny trousers.
She was also seen carrying a small black bag.
Carrie finished the look with a pair of black stilettos.
For today’s occasion, she opted for natural makeup and her signature loose wave hairstyle.
The mother-of-one completed the look with a discreet gold necklace with small stars and gold hoop earrings.
She was also seen wearing her stunning engagement and wedding ring and a few gold bracelets.
Carrie’s engagement ring is a large squoval emerald, set in platinum and diamonds, on a pave band.
The ring has been estimated by experts to be worth between £30,000 and £35,000.
James Constantinou, founder of Prestige Pawnbrokers of Channel 4’s Posh Pawn, said: “Boris Johnson’s traditional style is complemented by Carrie Symond’s love of vintage fashion.
“There is something utterly charming and romantic about buying antique jewellery and antique rings for engagement or eternity rings.”
It is unclear if Boris Johnson will join his wife and attend the event tonight.
Elena Bunbury, chairwoman of the LGBT+ Conservatives, said: “Carrie has always been a good sport to LGBT+ Conservatives.
“She even judged our virtual lip-sync last conference.
“We’re thrilled she’ll be joining us in person this year in Manchester.”
However, this is a rare appearance for Mrs Johnson, who doesn’t involve herself in politics.
Carrie was last seen earlier this summer during the G7 summit in Cornwall.