WASHINGTON — A judge in New Mexico on Tuesday ordered a county commissioner convicted of participating in the Jan. 6 riot at the Capitol removed from office under the 14th Amendment, making him the first public official in more than a century to be barred from serving under a constitutional ban on insurrectionists holding office.

The ruling declared the Capitol assault an insurrection and removed Couy Griffin, a commissioner in New Mexico’s Otero County and the founder of Cowboys for Trump, who was convicted earlier this year of trespassing when he breached barricades outside the Capitol during the attack. The judge’s order grabbed the attention of advocates across the country who have been pushing to use the 14th Amendment to disqualify former President Donald J. Trump and elected officials who worked with him in seeking to overturn the 2020 election from holding office in the future.

In his decision, Judge Francis J. Mathew of the New Mexico District Court said the insurrection on Jan. 6 included not only the mob violence that unfolded that day, but also the “surrounding planning, mobilization and incitement” that led to it.

“Mr. Griffin is constitutionally disqualified from serving,” the judge wrote.

Liberal groups have filed legal challenges in Arizona, New Mexico, North Carolina and Wisconsin seeking to block lawmakers accused of supporting the Jan. 6 rioters — including some prominent Republican members of Congress — from holding office under the Constitution. Until Tuesday, none had succeeded.

“This just went from being theoretical to being something that is legally recognized and legally possible,” said Noah Bookbinder, director of Citizens for Responsibility and Ethics, a nonpartisan watchdog organization that filed suit against Mr. Griffin on behalf of a group of New Mexico residents. “That’s hugely significant. It could have real implications for protecting the country from people associated with the effort to overturn the last election.”