Speaking at a WTO conference, International Trade Secretary Liz Truss said her country was preparing to seize "a golden opportunity."
Britain will be able "to determine our own trade policy for the first time in almost half a century and retake our seat at the WTO as a fully independent, sovereign nation," she said, according to a written version of her speech.
"For those of you worried about where we might have been for 45 years, let me reassure you: Britain is back."
Truss was addressing a closed-door event hosted by the International Chamber of Commerce, attended by British businesses such as BT and mining firm Anglo American, and diplomats.
In a statement released before her address, she claimed that "Britain is on the verge of taking back control of its trade policy."
"We live in an increasingly protectionist world and it is vitally important – now more than ever – that Britain and other WTO members fly the flag for free trade," she said.
Her comments came as Brexit talks between Britain and the European Union teetered on the brink of collapse just three weeks ahead of the deadline for finding a deal for an orderly departure.
Truss insisted in her address that Britain's exit from the bloc would be beneficial the country, and also for the international trading system, which currently finds itself under attack.
"We will use our new-found freedom to champion free, fair, rules-based international trade with the WTO at its centre," she said.
US President Donald Trump has repeatedly attacked the WTO and has launched bruising trade wars with China especially, but also with European allies.
Earlier this month, Washington announced that starting October 18, it would slap tariffs on $7.5 billion worth of European goods in retaliation against illegal subsidies for Airbus, with the tariffs hitting everything from French cheeses to Scotch whisky.
"Some may be content to live in a world of rising trade tensions and tit-for-tat tariffs, a world in which, for example, the good people of America are deprived of the chance to sample excellent Scotch whisky," Truss said.
"But this is not a world that I want to see, and when we take our independent seat around the WTO table, I can assure you we will be unapologetic in fighting the forces of protectionism, in favour of genuinely free trade."