Arsenal, Chelsea, Liverpool, Manchester City, Manchester United and Tottenham have linked up with six European clubs - three from Spain and three from Italy - to create a rival competition to the Champions League.
It is anticipated three more clubs will join the breakaway group as founding members with the new competition, which will begin "as soon as practicable" to eventually feature 20 teams.
A joint statement read: "Twelve of Europe's leading football clubs have today come together to announce they have agreed to establish a new midweek competition, the Super League, governed by its founding clubs.
"AC Milan, Arsenal, Atletico Madrid, Chelsea, Barcelona, Inter Milan, Juventus, Liverpool, Manchester City, Manchester United, Real Madrid and Tottenham Hotspur have all joined as founding clubs.
"It is anticipated that a further three clubs will join ahead of the inaugural season, which is intended to commence as soon as practicable."
The timing of the announcement is incendiary coming ahead of an anticipated announcement from UEFA confirming changes to the Champions League format on Monday.
The European governing body is expected to approve an increase from 32 to 36 teams from 2024 with the existing structure of eight groups of four replaced by one league. The format, known as the 'Swiss model', would see all teams play 10 games in the first stage with opponents determined by a seeding system.
The statement from the 12 clubs makes clear they do not believe these proposed changes go far enough.
It added: "The formation of the Super League comes at a time when the global pandemic has accelerated the instability in the existing European football economic model.
"Further, for a number of years, the founding clubs have had the objective of improving the quality and intensity of existing European competitions throughout each season, and of creating a format for top clubs and players to compete on a regular basis.
"The pandemic has shown that a strategic vision and a sustainable commercial approach are required to enhance value and support for the benefit of the entire European football pyramid.
"In recent months extensive dialogue has taken place with football stakeholders regarding the future format of European competitions.
"The founding clubs believe the solutions proposed following these talks do not solve fundamental issues, including the need to provide higher-quality matches and additional financial resources for the overall football pyramid."
It is proposed the new competition will be played in midweek with the eventual 15 founding members being joined by five qualifiers. It will be played initially in two groups of 10 with an eight-team knockout stage.
The organisers claim it will generate more money than the Champions League and that will result in a greater distribution of revenue throughout the game.
The statement added: "The new annual tournament will provide significantly greater economic growth and support for European football via a long-term commitment to uncapped solidarity payments which will grow in line with league revenues.
"These solidarity payments will be substantially higher than those generated by the current European competition and are expected to be in excess of €10billion during the course of the initial commitment period of the clubs."
News of the breakaway competition leaked out before it was officially announced and had already provoked a fierce backlash from UEFA and various national leagues and associations.
They pointed out the competition was unsanctioned and clubs and players risked bans by being involved.
World governing body FIFA also issued a strong condemnation after the announcement was made and called for further discussions.
The statement read: "In our view, and in accordance with our statutes, any football competition, whether national, regional or global, should always reflect the core principles of solidarity, inclusivity, integrity and equitable financial distribution.
"Moreover, the governing bodies of football should employ all lawful, sporting and diplomatic means to ensure this remains the case.
"Against this background, FIFA can only express its disapproval to a ‘closed European breakaway league' outside of the international football structures and not respecting the aforementioned principles."
It went on to call for unity and "all parties involved in heated discussions to engage in calm, constructive and balanced dialogue for the good of the game".
UEFA, along with the Football Associations of England, Spain and Italy, plus the Premier League, LaLiga and Serie A, said they would use all available means to stop the "cynical project".
A joint statement, issued before the later Super League announcement, read: "If this were to happen, we wish to reiterate that we will remain united in our efforts to stop this cynical project, a project that is founded on the self-interest of a few clubs at a time when society needs solidarity more than ever.
"We will consider all measures available to us, at all levels, both judicial and sporting in order to prevent this happening. Football is based on open competitions and sporting merit; it cannot be any other way.
"As previously announced by FIFA and the six federations, the clubs concerned will be banned from playing in any other competition at domestic, European or world level, and their players could be denied the opportunity to represent their national teams.
"We thank those clubs in other countries, especially the French and German clubs, who have refused to sign up to this. We call on all lovers of football, supporters and politicians, to join us in fighting against such a project if it were to be announced.
"This persistent self-interest of a few has been going on for too long. Enough is enough."
In a solo statement, the FA added the plan was "damaging to English and European football at all levels" and would "attack the principles of open competition and sporting merit which are fundamental to competitive sport". The Premier League also warned it would have a "deeply damaging impact".