Former state Sen. Brian Joyce was arrested Monday and charged in a federal indictment, the FBI said.

Joyce, a Milton Democrat, did not seek re-election last year after the launch of a federal probe into his alleged actions in the Senate to benefit his private law firm. He gave up his leadership positions during the investigation and maintained that he had committed no wrongdoing.

The Boston FBI office and U.S. Attorney's Office both posted about the arrest on Twitter before 8:30 a.m. Friday but did not include details of the charges.

Acting U.S. Attorney William Weinreb, FBI Special Agent in Charge Harold Shaw and IRS Special Agent in Charge Joel Garland plan to hold a 10:30 a.m. press conference Friday to discuss the charges against Joyce.

The FBI and IRS raided Joyce's Canton law office in February 2016.

Joyce was a senior member of former Senate President Stan Rosenberg's team before he relinquished his leadership roles.

Acting Senate President Harriette Chandler was elected by the Senate Monday to succeed Rosenberg while the Senate Ethics Committee conducts an investigation into whether the Amherst Democrat violated any Senate rules in connection with reports that his husband, Bryon Hefner, sexually assaulted three men with State House ties and interfered with Senate business. Rosenberg told the News Service Thursday that he hopes his name will be cleared.

Former Sen. Ben Downing, who served in the Senate with Joyce, reacted to the news of his former colleague's arrest. "Public service & elected office is a trust. When that trust is broken justice should be swift and harsh," Downing tweeted on Friday.

Joyce represented parts of Mattapan and Dorchester in the state Senate in the 1990s and early 2000s before redistricting pushed his seat further south in 2002.

Michael P. Norton contributed reporting.