Queen Elizabeth II, 91, boarded the ship at HM Naval Base in Portsmouth, and was accompanied by her daughter, Her Royal Highness The Princess Royal, Anne, 67.
At the ceremony to commission it into the Royal Navy Fleet, the Royal navy White Ensign was raised for the first time.
HMS Queen Elizabeth and its sister ship HMS Prince of Wales are the most expensive in the Royal Navy’s history.
Her Majesty stood out in a bright purple coat, which featured purple velvet buttons up the front, and purple velvet round the coat collar and sleeve cuffs.
As usual she wore a matching coloured round brim hat which has white and purple flowers resting on the front/
She kept warm with a pair of black gloves and skin-coloured tights, and accessorised with a black patent handbag and a silver and purple jewel brooch.
Princess Anne dressed in Royal Navy uniform
The Queen’s colour choice was very fashion-forward, as ultra violet has just been annouced as Pantone Colour of the Year 2018.
Around 3,700 guests attended the ceremony, which also saw Defence Secretary Gavin Williamson and First Sea Lord Admiral Sir Philip Jones in attendance.
Mr Williamson said the commissioning ceremony “marks the start of a hugely significant chapter for the Royal Navy”.
He added: “It is an honour to witness the crowning moment of an extraordinarily busy year for the Royal Navy that has seen us name the second carrier, HMS Prince of Wales, cut steel on the first Type 26 frigates and launch the National Shipbuilding Strategy.
“Our new aircraft carrier is the epitome of British design and dexterity, at the core of our efforts to build an Armed Forces fit for the future.
“For the next half a century both carriers will advance our interests around the globe, providing the most visible symbol of intent and commitment to protect the UK from intensifying threats, wherever they may come.”
He told the Press Association: “It is absolutely relevant, HMS Queen Elizabeth will be serving in the Royal Navy for the next 50 years.
“The final captain of this ship has yet to be born.
“We have been working, the Navy have been working, the Ministry of Defence have been working to get it ready for the last 20 years.
“This is a very important moment.”