Grant Thornton has agreed to acquire rival firm CBIZ in a $5 billion cash transaction, marking the largest takeover in the accounting sector in over two decades. The deal, announced on Wednesday, will create the largest US audit and consulting firm outside of the Big Four, with combined annual revenue exceeding $5 billion.

The acquisition reflects ongoing consolidation within the mid-market accounting space, driven in part by private equity investment. Grant Thornton, which sold a majority stake to New Mountain Capital in 2024, has pursued an aggressive acquisition strategy but had been surpassed in revenue growth by competitors such as Baker Tilly, another private equity-backed firm.

CBIZ, established nearly 30 years ago as the only publicly listed audit firm in the United States, has expanded significantly in recent years, including its 2024 purchase of Marcum, a firm known for auditing US public companies. CBIZ currently ranks as the eighth-largest US accounting firm by revenue, with Grant Thornton placed ninth. The newly combined entity will overtake RSM, which reported $4.9 billion in revenue last year.

With more than 9,500 employees nationwide, CBIZ has historically concentrated on small and medium-sized businesses as well as individual clients. Grant Thornton operates as part of a global network comprising multiple firms, many of which share ownership ties with New Mountain Capital. Following the closing of the deal, New Mountain plans to separate CBIZ’s non-accounting operations into an independent company.

Grant Thornton Chief Executive Jim Peko stated that the merger would enhance the firm’s ability to support businesses at various stages of growth, from early development to international expansion.

Under the terms of the agreement, CBIZ shareholders will receive $5 per share in cash, representing a premium of 18 percent over CBIZ’s closing price on Tuesday and 54 percent above its 30-day average. This valuation, which includes debt, places the enterprise value of CBIZ at $5 billion, although it remains significantly below the peak share price of $88.65 reached early last year.

This transaction represents the largest consolidation in the accounting industry since the 1998 merger of Price Waterhouse and Coopers & Lybrand, which formed one of the Big Four firms still dominant today.