Miller, Coors Light and Grolsch firm SABMiller said Budweiser maker Anheuser-Busch InBev was planning a takeover bid for the group.
SABMiller confirmed rival Anheuser-Busch had informed it that it was preparing to table an offer, ending months of speculation over a possible bid for the FTSE 100 listed firm.
Shares in SABMiller surged nearly 20% higher after the news.
SAB said it had not yet received any bid proposal from AB InBev and did not have any details of the planned approach.
"The board of SABMiller will review and respond as appropriate to any proposal which might be made," it added in a brief statement.
AB InBev said that it wanted to work towards a friendly bid.
"AB InBev's intention is to work with SABMiller's board toward a recommended transaction," it said.
But SABMiller urged shareholders to sit tight and "take no action" in the absence of any firm bid.
Anheuser-Busch InBev now has until 5pm on October 14 to make an offer or walk away under a "put up or shut up" deadline set by the City Takeover Panel.
A merger of the two firms would bring together two of the world's biggest beer groups, with AB InBev potentially adding SABMiller's Peroni and Grolsch brands to its own stable of more than 200 beers, including Corona and Stella Artois, Beck's, Leffe and Hoegaarden.
SABMiller employs around 69,000 people in more than 80 countries and has global annual sales of more than $26bn.
It claims more than 140,000 bottles of SABMiller beer are sold every minute of every day.
Its suitor and larger rival AB InBev, which is based in Leuven, Belgium, has a 155,000-strong global workforce and makes more than US$47.1bn in global revenues.
A tie-up between SAB and AB InBev could create a combined business worth around US$280bn
SAB attempted to acquire Heineken a year ago, but its advances were rebuffed.
Experts believe the move would have strengthened its defences against a takeover bid by AB InBev.