The former publisher of The National Enquirer testified on Monday before the Manhattan grand jury hearing evidence about Donald J. Trump’s role in a hush-money payment to a porn star, according to people with knowledge of the matter.

The publisher, David Pecker, also testified in January, soon after the grand jury was impaneled by the Manhattan district attorney, Alvin L. Bragg. The grand jury has heard from at least nine witnesses — including Mr. Pecker, who has gone in twice — and is expected to vote on an indictment soon.

Mr. Pecker, who was seen leaving the building where the grand jury sits at about 3:30 Monday afternoon, was a key player in the hush-money episode. He and the tabloid’s top editor helped broker the deal between the porn star, Stormy Daniels, and Michael D. Cohen, Mr. Trump’s fixer at the time.

Ever since Mr. Trump predicted his arrest a little more than a week ago, all eyes have turned to the grand jury, which operates in secret.