The beaming couple emerged from the grey-stone Old Marylebone Town Hall to confetti and cheers from dozens of fans who had waited hours to catch a glimpse of the music legend and his new wife.
Brunette Shevell, 51, wore a knee-length, long-sleeved white dress which reports said was designed by McCartney's fashion designer daughter Stella.
The bride also had a white flower in her hair and carried a small posy of roses, while "Hey Jude" singer McCartney wore a dark suit and light blue tie. One newspaper had a headline saying: "Yes-today", in a reference to the famous Beatles song.
Despite his huge wealth as a key songwriter and frontman for the world's most successful pop band, 69-year-old McCartney chose a modest civil ceremony before a small group of family and friends.
Ringo Starr, the only other surviving member of the "Fab Four", and his wife Barbara Bach were among the guests at the wedding. Ex-Beatle John Lennon, who was assassinated in New York in 1980, would have been 71 on the day of the wedding.
After the ceremony, which lasted just over an hour, the newlyweds returned to McCartney's home in St. John's Wood for an evening reception.
The property in the upmarket area of north London is just a few streets away from the Abbey Road Studios where the Beatles recorded many of their most famous songs.
Asked how he felt after marrying for a third time, he told reporters: "Terrific, thank you. I feel married. I feel absolutely wonderful."
Rock'n'roll royalty including Starr, Rolling Stone Ronnie Wood and guitarist Jeff Beck attended the reception, as did model Twiggy and artist Tracey Emin.
Late Beatle George Harrison's widow Olivia turned up to the soiree, which was also designed to be a low-key affair.
McCartney's spokesman declined to divulge any details of the wedding day, but celebrity-hungry tabloids in Britain, where the affectionately named "Macca" is hugely popular, have been poring over every detail.
According to reports, McCartney composed a song for Shevell especially for their big day.
He was also expected to perform "Let it Be", which he sang to Shevell on one of their first holidays together three years ago, and her favorite "Let Me Roll It", the Sunday Mirror said.
McCartney was married for 29 years to American photographer Linda until her death from breast cancer in 1998. He said at the time that he and Linda had spent just 11 nights apart during their marriage.
McCartney's marriage to former model and charity campaigner Heather Mills was less happy.
The couple wedded in 2002 in a lavish ceremony at Castle Leslie in Ireland estimated by celebrity magazines to have cost around $3.2 million.
But four years later they confirmed they had separated, blaming media intrusion into their private lives, and in 2008 the couple divorced.
A judge had to rule on the size of the divorce settlement after the couple failed to reach agreement themselves, and Mills was awarded 24.3 million pounds ($38 million), ending one of the most acrimonious breakups in showbusiness history.
She had claimed 125 million pounds and said McCartney was worth 800 million pounds, although a judge found his fortune was worth half that amount.
McCartney has a son, two daughters and a stepdaughter from his marriage to Linda, and a daughter from his marriage to Mills.
The independently-wealthy Shevell, who was married to an attorney for more than 20 years and serves on the board of New York's Metropolitan Transportation Authority, has a son.