HMS Duncan, a Type 45 destroyer, was commissioned into the Navy on September 26 and was expected to be handed over to the fleet in the spring.
But preparations for the 7500-tonne vessel have been achieved faster than planned and the warship has now joined the fleet alongside its sister ships, which are the UK's most advanced warships.
Defence, Equipment, Support and Technology Minister Philip Dunne said: "Thanks to the skill and hard work of the commanding officer, the ship's company and their MoD and industry partners, HMS Duncan has entered service four months early.
"It is testament to the improving control of projects across the armed forces and significant dedication across defence that all six ships of the Type 45 class are now in the hands of the Royal Navy.
"We expect these vessels to see decades of service protecting the UK's interests around the world, including providing humanitarian aid as we saw recently with HMS Daring's efforts in the Philippines."
Commander James Stride, HMS Duncan's commanding officer, said: "The ship's company is rightly proud to be on board such a cutting edge warship.
"HMS Duncan joins the Royal Navy as the most advanced ship we have ever operated alongside the rest of the Type 45 class, able to operate across the globe protecting the fleet."
Duncan will now embark on a programme of trials to prepare the ship and crew for operational deployment.
Its handover to the fleet marks the end of a 13-year build programme with BAE Systems to deliver the six ships - Daring, Dauntless, Diamond, Dragon, Defender and Duncan.