The Democratic governor of Illinois, JB Pritzker, will headline a major Democratic fundraiser in New Hampshire on Sunday as the potential 2028 presidential contender builds his national profile and positions himself as a leading voice opposing President Trump.

Mr. Pritzker has given several high-profile speeches this year criticizing Mr. Trump, but the keynote address at the New Hampshire Democratic Party’s McIntyre-Shaheen 100 Club Dinner could be the most prominent. The annual event stands out among state Democratic fundraisers thanks to New Hampshire’s role in holding the nation’s first presidential primary.

Mr. Pritzker will “address rising authoritarianism and the need for Democrats to fight back,” according to a statement from his spokesperson, Jordan Abudayyeh.

The second-term governor has yet to say whether he will run for that office again in 2026, but the billionaire Hyatt heir has been laying the groundwork for a potential presidential campaign for years.

Mr. Pritzker drew national attention in February when he used part of his joint budget and State of the State address to argue for a parallel between Mr. Trump’s rhetoric and the rise of Nazi Germany. Since then, the governor has spoken at the Human Right Campaign’s Los Angeles dinner and is scheduled to headline a Minnesota Democratic-Farmer-Labor Party dinner in June.

Mr. Pritzker has carved out a distinct position among Democratic governors viewed as potential 2028 candidates.

Michigan’s Governor Whitmer has sought common ground with Mr. Trump, appearing alongside him multiple times early in his second term. Governor Newsom of California has launched a podcast featuring friendly conversations with Trump loyalists, including Steve Bannon.

Mr. Pritzker was a keynote speaker at the New Hampshire Democratic Party’s 2022 convention, which at the time also fueled speculation he was looking toward a national post. He was elected to his second term as governor that year.

Last year’s featured speaker at the McIntyre-Shaheen 100 Club dinner was Governor Walz, who went on to become the vice presidential nominee. The first 100 Club dinner was held in 1959 to promote the presidential candidacy of John F. Kennedy. In 2020, speakers included 10 Democratic candidates for president.