The signatories, which include the UK, the US, EU, and China, are a minority of the WTO's 164 members, but represent 90% of all services trade.
Banking, information technology, telecoms, architecture, and engineering are among the service sectors which could benefit most from the deal.
International policy forum the Organisation for Economic Co-operation and Development (OECD) has estimated that implementing looser regulations in G20 countries could reduce trade costs by up to 6%.
The Department for International Trade said the new rules would make it easier for businesses, in particular small and medium-sized firms, to navigate foreign markets and obtain authorisation to export overseas.
The European Services Forum (ESF), which represents the interests of the European service sectors, welcomed the agreement announced in Geneva, saying it had called for such regulation for more than 20 years.
The WTO aims to bring the new rules into force in 2023.
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