Prime Minister Theresa May is to officially notify the European Union on March 29 that the UK is leaving.
Downing Street said she would write a letter to the European Council, adding that it hoped negotiations on the terms of exit and future relations could then begin as quickly as possible.
Mrs May's spokesman also rejected reports an early election may be held. Under the Article 50 process, talks on the terms of exit and future relations are not allowed until the UK formally tells the EU it is leaving.
If all goes according to the two year negotiations allowed for in the official timetable, Brexit should happen in March 2019.
The Prime Minister was in Wales as part of ongoing engagement with devolved nations ahead of triggering Article 50. As part of a series of visits around the UK – including to Wales, Scotland and Northern Ireland - the Prime Minister will be engaging and listening to people from right across the nation as we prepare to leave the EU as one United Kingdom.
This comes as Swansea signs its historic City Deal which is expected to create more than 9,000 jobs and trigger almost £1.3 billion in investment. The deal formed between the UK Government, local authorities and the Welsh Government, paves the way for major infrastructure investment in the Swansea City Bay region, ranging from research centres to a new waterfront “digital district”.
During the visit, the Prime Minister, accompanied by the Secretary of State for Exiting the EU and the Secretary of State for Wales, will meet with First Minister Carwyn Jones as well as representatives from a range of sectors and businesses.
The main point of discussion will be how every part of the UK – including Wales - can make the most of the opportunities offered by Brexit. The Welsh export market is worth around £12.3 billion a year – showing that there has never been a better time for Welsh companies to export overseas.
Wales is already a successful exporter – shipping aircraft wings to the world, cooling technology to the Middle East and TV formats to dozens of countries.
Prime Minister Theresa May said: "From my first day on the steps of Downing Street, I made clear my determination to strengthen and sustain the precious Union. I have also been clear that as we leave the European Union I will work to deliver a deal that works for the whole of the UK.
"I want every part of the United Kingdom to be able to make the most of the opportunities ahead and for Welsh businesses to benefit from the freest possible trade as part of a global trading nation.
"Wales’ universities already have an excellent international reputation, attracting overseas students and pioneering in research projects here and abroad.
"I also want Wales to be at the forefront of science and innovation – as demonstrated by today’s landmark City deal for Swansea.
"The deal is a great example of what can be achieved when the UK Government, the Welsh Government and local authorities work together to secure a deal that benefits the city and the whole of Wales.
"This government’s Plan for Britain will seek to deliver a stronger, fairer United Kingdom and a better deal for ordinary working people in Wales and across the nation."
