Doug Mastriano names Jenna Ellis, a former Trump campaign lawyer, as a senior legal adviser.

Doug Mastriano, the Republican nominee for governor in Pennsylvania, has appointed Jenna Ellis, a former lawyer for the Trump campaign who worked to overturn the 2020 election, as a senior legal adviser, his campaign announced on Tuesday.

Ms. Ellis campaigned vigorously during the primary for Mr. Mastriano, who played a key role in efforts in Pennsylvania to subvert the state’s 2020 results in favor of former President Donald J. Trump.

In effect, the appointment means that a lawyer who sought to shake the pillars of American democracy is joining forces with a candidate who could soon hold significant sway over the appointment of presidential electors and the certification of election results in one of the most critical battleground states.

“The talent, experience and legal expertise Jenna brings will be an important factor in helping us defeat Josh Shapiro and the extreme Democrat agenda in November,” Mr. Mastriano said in a statement, referring to his Democratic opponent, the state’s attorney general.

Ms. Ellis, along with Rudolph W. Giuliani, was the public face of the Trump campaign’s effort to overturn the 2020 election, appearing frequently at news conferences and on television to promote false allegations of voter fraud. She called the Trump legal team an “elite strike force,” and has boasted of being a protégé to Mr. Giuliani.

On the primary campaign trail this year, Ms. Ellis pointed to Mr. Mastriano’s efforts in November 2020, when, as a freshmen state senator, he organized a hearing featuring members of Mr. Trump’s legal team, including Ms. Ellis and Mr. Giuliani, to spread false claims about the election. Mr. Mastriano also pressured Justice Department officials to open inquiries into the election.

Few Republican candidates for governor have made overhauling elections as central to their platform as Mr. Mastriano has. He has called for forcing Pennsylvanians to re-register to vote — a policy some legal experts have said is illegal — and he wants to decommission some election machines.

“Doug Mastriano, I like to say, is the Donald Trump of Pennsylvania,” Ms. Ellis said at a campaign event in Erie last month.