The lawsuit, which seeks damages on behalf of publishers of websites and apps based in the United Kingdom, is the latest case to focus on the search giant's business practices.
Ad Tech Collective Action is bringing the claim on behalf of publishers who say they have suffered losses due to Google's allegedly anti-competitive behaviour.
Google last month urged the CAT to block the case, which it argued was incoherent. The company "strongly rejects the underlying allegations", its lawyers said in court documents.
The CAT said in a written ruling that it would certify the case to proceed towards a trial, which is unlikely to take place before the end of 2025.
The tribunal also emphasised the test for certifying a case under the UK's collective proceedings regime - which is roughly equivalent to the United States' class action regime - is relatively low.
Google did not immediately respond to a request for comment.
Ad Tech Collective Action's case comes amid ongoing probes by regulators into Google's adtech business, including by Britain's Competition and Markets Authority and the European Commission.
Google is also fighting two lawsuits in the United States, one brought by the Department of Justice and another by Texas and other states, accusing the company of anti-competitive conduct.
Google's lawyers said in documents for the CAT case that the company's "impact in the ad tech industry has been hugely pro-competitive".
Wednesday's decision is the latest against a tech giant to be given the green light by the CAT, which already this year has certified a $US3.8 billion case against Facebook parent Meta and a nearly $US1 billion case against Apple.
