Oklahoma Gov. Kevin Stitt on Tuesday appointed energy executive Alan Armstrong to the U.S. Senate, filling the vacancy created by Sen. Markwayne Mullin’s move to lead the Department of Homeland Security. Armstrong will serve the remainder of the term through 2026 but, under state law, is not eligible to run for the seat in the upcoming election.

Armstrong, 63, is the chairman and former CEO of Williams Companies, a Tulsa-based pipeline operator specializing in natural gas infrastructure. He spent decades with the company, serving as president and CEO beginning in 2011 before transitioning to executive chairman last year.

Stitt said the appointment reflects his commitment to selecting a conservative leader with private-sector experience. He described Armstrong as a business-focused figure who supports free markets and limited government, aligning with the state’s economic priorities.

Armstrong has not previously held elected office but said his focus in the Senate will include advancing permitting reform for large-scale infrastructure projects. He argued that regulatory hurdles have made it increasingly difficult to build critical energy systems, which he said are essential to maintaining long-term U.S. competitiveness.

The appointment comes as Rep. Kevin Hern, a Republican from Oklahoma, has already launched a campaign for the seat and secured an endorsement from former President Donald Trump. Armstrong said he has met with Trump and credited his working relationships with administration officials, including Interior Secretary Doug Burgum and Energy Secretary Chris Wright, with helping build support.

Armstrong has been a political supporter of Stitt, contributing the maximum allowable amount to his campaigns since 2018. His selection also follows recent tensions between Stitt and Trump over disagreements tied to the National Governors Association, which Stitt currently leads.

Supporters of the appointment pointed to Armstrong’s experience in the energy sector as a key asset, particularly as global energy markets face instability tied to international conflicts. Former Tulsa Mayor Dewey Bartlett Jr. described Armstrong as a consensus-driven leader with deep knowledge of the oil and gas industry.

Mullin was confirmed Monday as Secretary of Homeland Security, replacing Kristi Noem after mounting criticism over immigration enforcement policies. His departure created the Senate vacancy that Armstrong will now temporarily fill.