His tweet came in tandem with a press conference which he attended along with European Commission President Jean-Claude Juncker and visiting Japanese Prime Minister Shinzo Abe.
Theresa May will trigger Article 50 on 29 March, her office announced today (20 March), starting two-years of unprecedented negotiations for a country to leave the 28-member bloc for the first time.
Donald Tusk, the head of the European Council, said that within 48 hours of the triggering of Article 50, he would present draft guidelines to the remaining 27 member states.
Britain voted in a referendum last year to break away from the EU after a more than 40-year-long membership in the bloc and its predecessor, the European Economic Community.
Barnier said the first condition for success was the unity of the 27 governments staying in the European Union and the transparency of the negotiations.
If no deal is reached by the end of the period, the United Kingdom will crash out of the European Union with no deal and revert to World Trade Organisation rules.
"Next Wednesday, the government will deliver on that decision and formally start the process by triggering Article 50", he said.
Brexit Secretary David Davis is facing questions in Parliament ahead of the Government formally giving the European Union its notice to quit the bloc next week.
Elaborating on the memo that will kick-start the Article 50 process on March 29, Mrs May indicated her message to European Union leaders will contain substantial detail of her negotiating intentions as she declared it will "set the tone" for Britain's new relationship with Europe.
House of Commons speaker John Bercow announced the news to MPs, and PM May's May's spokesman told a briefing: "We look forward to beginning negotiations when we trigger Article 50 by the end of this month".
An EU spokesman said it was "ready and waiting" for the letter. Exiting EU has been one of the most crucial decision for United kingdom because it will directly affect the economy of the country, its students and people studying and working in other EU related countries and trade activities if it would be smooth and free as earlier it was when United kingdom was part of EU.
The committee's report is entitled Brexit: justice for families, individuals and businesses? .
"The sooner we reach a deal on an orderly withdrawal, the sooner we can prepare for the future relationship", he said, adding that leaving hard divorce issues until the last moment was playing with failure.
What follows will be a two-year negotiation period to agree on a potential exit deal.
The meeting will be used to agree the guidelines for the EU's negotiating team headed by Michel Barnier.
Mr Barnier has set a target of October 2018 for the withdrawal talks to be wrapped up, allowing six months for the agreement to be ratified by the EU's parliaments.