It has taken just two years to scale up. Having opened up its capital to private equity in 2024, Grant Thornton is set to complete the largest acquisition in the US accountancy sector for more than 25 years. Grant Thornton Advisors has entered into a definitive agreement to acquire CBIZ, a professional services group listed on the New York Stock Exchange. The deal values the company at $5bn, including debt. CBIZ shareholders will receive $55 per share in cash, representing a premium of 17.8% over the last closing price and 54% over the weighted average of the previous 30 trading sessions.

The transaction is still subject to approval by CBIZ’s shareholders and the necessary regulatory authorisations. It is expected to be finalised in the fourth quarter of 2026. The agreement also includes a ‘go-shop’ clause: CBIZ may seek a higher offer until 27 August.

The merger will make Grant Thornton the fifth-largest US provider of professional, tax and advisory services, behind Deloitte, PwC, EY and KPMG. The new entity will generate more than $5bn in revenue in the United States.

Nearly 10,000 employees in the United States

CBIZ brings with it more than 9,500 employees and a presence in 23 major US markets. The group operates in the fields of accountancy, taxation and consultancy, as well as insurance, employee benefits and technology. It had already expanded significantly by acquiring Marcum for $2.3bn in 2024.

Grant Thornton is therefore acquiring a consolidator rather than a traditional, stand-alone firm. Once the transaction has been completed, CBIZ will be delisted and will become a wholly-owned subsidiary of Grant Thornton Advisors.

However, not all of its activities will remain within the group. CBIZ’s Benefits and Insurance Services division is to be spun off to form an independent company, which will continue to be backed by New Mountain Capital. Grant Thornton will primarily retain the business lines that strengthen its accounting, tax and advisory platform.

A billion for AI

The New York-based fund is the real financial driving force behind the merger. In May 2024, New Mountain Capital led the investment that enabled it to take control of Grant Thornton Advisors. The Caisse de dépôt et placement du Québec and OA Private Capital invested alongside it at the time as minority shareholders. New Mountain is now providing fresh equity capital to finance the acquisition of CBIZ.

The deal illustrates the transformation of mid-market accountancy firms into acquisition platforms. Private equity investment provides them with the means to finance acquisitions, technological investments and greater international integration. Grant Thornton Advisors has, in particular, announced a $1bn programme dedicated to artificial intelligence and advanced technologies.

However, the structure is based on a legal separation required by US rules on audit independence. Grant Thornton LLP, a firm organised in accordance with the professional standards applicable to chartered accountants, retains responsibility for audit and assurance engagements. Grant Thornton Advisors LLC, which is not a registered audit firm, covers tax, advisory and other services. It is this second entity that is acquiring CBIZ and receiving investment from New Mountain.

This is therefore not an acquisition carried out directly by Grant Thornton International. The global network comprises legally separate firms in over 150 markets. At the same time, Grant Thornton Advisors has established a multinational platform bringing together nearly 20 firms aligned around common standards, technologies and service capabilities, without merging them into a single global company.

With CBIZ, this platform will report revenue of nearly $7.5bn, more than 34,500 professionals and a presence in over 20 countries and territories. These figures extend beyond the US alone, but do not represent a consolidation of the entire Grant Thornton International network.

The transaction therefore does not entail any announced changes to Grant Thornton Luxembourg’s capital structure. It may, however, strengthen the technological, sector-specific and cross-border resources to which the firms associated with the US platform will have access.