• The duke had appeared relaxed as he arrived at the abbey and was seen chatting to his cousins Princess Beatrice and Princess Eugenie.
• It is thought it is the first time he has seen his family since his controversial memoir, Spare, came out.
The Duke of Sussex was part of the congregation as his father King Charles III was crowned at Westminster Abbey.
Prince Harry watched intently from his seat in the third row as the crown was held above above the King's head.
The duke had appeared relaxed as he arrived at the abbey and was seen chatting to his cousins Princess Beatrice and Princess Eugenie.
It is thought it is the first time he has seen his family since his controversial memoir, Spare, came out.
After the ceremony Prince Harry was seen getting into a car alone.
It is not known if he was heading for Buckingham Palace or to an airport, as he reportedly plans to return to the US to celebrate his son's birthday.
His uncle Prince Andrew left in a car behind, with Princess Eugenie and her husband.
Earlier, when Prince Harry entered the abbey, dressed in a morning suit and wearing medals, he appeared relaxed and was seen smiling at guests as he walked down the nave of the abbey, before chatting to several family members.
He tapped Princess Beatrice's husband Edoardo Mapelli Mozzi on the back with a smile on his face, before taking his place beside Jack Brooksbank - husband of Princess Eugenie - in the third row. Also in the third row was the Duke of York, Prince Andrew.
He watched the ceremony behind the King's sister Princess Anne and the Duke of Kent, Queen Elizabeth II's first cousin, dressed in Garter robes on the second row.
Ahead of them were the Prince and Princess of Wales and their children Princess Charlotte and Prince Louis, as well as the King's brother the new Duke Edinburgh - Prince Edward - and his wife Sophie.
Previously, Prince Harry had been seated in the second row - directly behind the King - at Westminster Abbey for the late Queen Elizabeth's funeral last year.
The prince was seen in television footage watching intently as the archbishop raised St Edward's Crown above his father's head during the Coronation.
Later, when the congregation paid homage to the new monarch, Prince Harry was seen along with other royals saying the words: "God save King Charles. Long live King Charles. May the King live forever."
After landing at London's Heathrow Airport on Friday morning, the prince reportedly stayed at Frogmore Cottage on the grounds of Windsor Castle - the residence he and Meghan were asked to vacate by the King.
His wife, the Duchess of Sussex, has remained in Los Angeles with their children, where their son Prince Archie will be celebrating his fourth birthday.
A source told the US outlet Page Six that Prince Harry intended to make "every effort to get back in time for Archie's birthday".
Last month Buckingham Palace confirmed that Prince Harry would attend the ceremony alone.
However, officials said Prince Harry and his uncle Prince Andrew would have no formal role in the ceremony, as they are not working members of the Royal Family.
Unlike other members of the family, Prince Harry did not wear robes or military uniform - despite the fact that he served in the army for a decade, including two tours of Afghanistan.