Grant Thornton has agreed to acquire rival CBIZ for $5bn in cash, marking the largest takeover in the accounting sector in a generation. This deal will position Grant Thornton as the biggest audit and consulting firm in the US outside the Big Four.

The acquisition underscores the rapid consolidation occurring in the mid-market accounting sector, fueled by private equity. Grant Thornton has been actively acquiring companies since selling a majority stake to New Mountain Capital two years ago. CBIZ, a long-standing public accounting firm, also recently bolstered its operations by acquiring Marcum in 2024.

CBIZ is currently the eighth-largest US firm by revenue, with Grant Thornton in ninth. The combined entity is projected to surpass RSM, establishing itself as a significant player. The deal values CBIZ at $5bn, offering a premium to its shareholders. Jim Peko, Grant Thornton’s chief executive, stated the merger will broaden their capacity to support businesses of all sizes. New Mountain Capital plans to separate CBIZ's non-accounting divisions post-acquisition.