The deal excludes Grant Thornton Ireland’s audit business. Credit: M Isolation photo/Shutterstock.

US-based Grant Thornton Advisors and Grant Thornton Ireland have agreed to combine their advisory and tax services.

Grant Thornton Advisors, a tax and advisory services provider, and Grant Thornton Ireland, have reported annual revenues of $2.4bn and €300m ($333m), respectively, in 2023.

The combination is backed by New Mountain Capital, which manages around $55bn in assets.

Expected to close in the first quarter of 2025, the transaction awaits regulatory approval.

Upon completion, the combined entity will offer a full suite of advisory and tax solutions.

This deal excludes Grant Thornton Ireland’s audit business, which will remain an independent partnership running under an alternative practice structure.

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The independent audit business will continue to offer assurance services.

Grant Thornton Advisors CEO Seth Siegel will lead the combined business. Steve Tennant will serve as the president of Grant Thornton Ireland and will join the executive committee.

Grant Thornton Advisors CEO Seth Siegel said: “This is a landmark year, as we’re commemorating Grant Thornton’s 100th anniversary in the US, and I can’t think of a better way to do it than by spearheading a seamless and integrated global platform with Grant Thornton Ireland — one that puts us in the vanguard of high-growth and high-quality firms.

“We share a common focus on client centricity, culture and delivering the highest quality results on a global scale. This strategic move signals a pivotal time in our industry that enables our clients to benefit even more from our innovative services with industry-leading execution, and bolsters accelerated and meaningful career-growth opportunities for all our professionals.”

Simpson Thacher & Bartlett, William Fry, and Arthur Cox served as advisers for Grant Thornton Advisors and New Mountain Capital.

Deutsche Bank Securities was the financial advisor for Grant Thornton Ireland, with A&L Goodbody providing legal counsel.