US accounting firm Grant Thornton has named Storme Sixeas as the new leader of Tax Legislative Affairs in its Washington National Tax Office (WNTO).

In the new role, Sixeas will offer strategic guidance on tax legislative matters to clients, the company said.

With a career spanning more than 20 years in Washington, Sixeas specialises in offering insights on federal tax policy and the political environment to a diverse array of industries and taxpayers.

Prior to Grant Thornton, Sixeas served at Deloitte’s Washington National Tax office for nearly ten years, advising on federal tax policy.

Her career also includes roles as a policy lobbyist for BAE Systems and the Electronic Industries Alliance, and as a leadership aide in the House of Representatives.

Grant Thornton Tax Services national managing principal Mark Margulies said: “In today’s ever-evolving tax legislative landscape, bringing an in-depth point of view and adaptable solutions is essential to staying ahead of trends and ultimately delivering exceptional client service.

GlobalData Strategic Intelligence

US Tariffs are shifting - will you react or anticipate?

Don’t let policy changes catch you off guard. Stay proactive with real-time data and expert analysis.

By GlobalData

“Storme’s experience as a trusted tax adviser, paired with her legislative and advocacy background, uniquely positions her to help our clients navigate complexity and drive meaningful results.”

Grant Thornton operates in the US through two entities: Grant Thornton for audit and assurance services, and Grant Thornton Advisors for tax and advisory services.

The firm recently expanded its global reach by forming a platform through the merger of US-based Grant Thornton Advisors and Grant Thornton Ireland’s advisory and tax services.

It incorporated Grant Thornton UAE and Grant Thornton Netherlands in April and May 2025, respectively.

The multinational platform has $2.7bn in revenues, nearly 60 offices, and almost 13,000 professionals.

The latest development comes after Grant Thornton introduced CompliAI, a new AI-powered solution designed to enhance compliance processes within its service delivery teams.