The duchess, who is usually accompanied by her husband Prince William, sat with Mr Middleton to see Novak Djokovic beat Matteo Berrettini.
She wore a baby pink belted dress by Beulah London, cream Aldo heels and a colourful face mask for the final day of the two-week tournament.
At one point the duchess laughed as she took part in a Mexican wave.
Mission Impossible star Tom Cruise returned to SW19 for the men’s final, having watched the women’s match a day earlier.
England football captain Harry Kane revealed this weekend that Cruise called the team to wish them well in their historic match, although he said he did not know if the Top Gun actor would be at Wembley.
On Saturday, for the women’s final, Kate had attended with her husband the Duke of Cambridge.
It is a big weekend of sport for the couple, with keen tennis fan Kate patron of the All England Lawn Tennis Club, while William is president of the Football Association.
On Saturday, Kate presented trophies to the winner of the ladies singles Ash Barty yesterday and runner up Czech finalist Karolina Pliskova.
She later congratulated the duo on Twitter for playing an "incredible match".
The duchess tweeted: "It was amazing to see the atmosphere and support from the fans echoing through centre court once again."
It was the duchess’s first outing since she was forced to self-isolate after coming into contact with a person with Covid.
She isolated for seven days before returning to public engagements on Saturday afternoon.
It is a big weekend of sport for the couple, with William expected attend Wembley Stadium on Sunday night for England’s historic clash with Italy in the Euro 2020 final.