At 158,000 tonnes, the Freedom of the Seas offers a pool with artificial waves for surfers, an ice rink and cantilevered whirlpools that extend out from the sides of the ship, 112 feet above the sea.
The vessel, which will sail next Wednesday for New York before heading to its Miami base from where it will ply the Caribbean trade, wrested the crown as the worlds biggest liner from the 151,000-tonne Queen Mary 2 launched over two years ago.
The ship can hold over 3,600 guests, is 15 decks high and is the length of 37 buses.
The gleaming white vessel edged into Southampton port, southern England on a sunny morning on Saturday and will be welcomed with fireworks display in the evening.
The vessel will entertain guests including VIPs and travel journalists in Southampton before travelling to New York, where a naming ceremony will take place.
But Freedoms time at the top may be short-lived amid talk of even larger ships. A vessel codenamed Project Genesis is already set to make an appearance in 2009 at 220,000 tonnes.
The US-Norwegian owners Royal Caribbean say Freedom of the Seas was designed to appeal to the broadest consumer base possible.
But although the industry appears committed to building ever-larger ships, there is disquiet among some operators that vessels are becoming too big and the market too crowded.
Earlier this month, the head of rival Carnival said it was shifting away from the dominant Caribbean market which has been weakened recently by hurricane fears and lower demand. Carnival said it would shift focus towards the Alaskan and European markets.