"Today is an important step on the road to delivering a smooth and orderly Brexit and forging our deep and special future partnership," May said Friday on Twitter, thanking European Commission President Jean-Claude Juncker and EU President Donald Tusk.
EU leaders on Friday approved the opening of the next stage of Brexit talks after reaching a deal on divorce terms with Britain, Tusk said.
"EU leaders agree to move on to the second phase of Brexit talks. Congratulations PM @theresa_may", Tusk tweeted.
At a meeting in Brussels, members of the bloc said there has been enough progress on key issues. The next phase will involve discussions over future relations and trade ties between the UK and the EU.
Echoing Tusk’s comments regarding May, "She was tough, smart, polite and friendly negotiator" Juncker said.
Negotiations on the transition period will resume in January.
But talks on trade will not begin until March as EU members need more clarity on the UK’s post-Brexit plans.
May signed the divorce deal with Juncker on December eight after months of negotiations. The deal covers Britain's exit bill, the future of the Irish border and the rights of EU expatriates in the UK.
Earlier on Wednesday, EU chief Brexit negotiator Michel Barnier said there will be "no turning back" for Britain on commitments made during an initial divorce deal between the two.
Meanwhile, the government argues that the changes could endanger the chances of delivering a smooth departure from the EU, noting however that the "minor setback" would not prevent the UK leaving the EU in 2019.