The Friday raids were carried out by the U.S. attorney's office, FBI, IRS and state police. Boxes of evidence were carried off, but officials have not said whom or what they are investigating.
Fox has represented Rhode Island's capital in the General Assembly for more than 20 years, and became the nation's first openly gay House speaker when he assumed the post in 2010. He came out in 2004, in an unplanned announcement, while addressing a gay marriage rally at the Statehouse.
The raids almost immediately set off jockeying Friday among members of the House vying to become the next speaker. On Saturday, shortly after Fox's announcement, his top deputy said he intends to run for speaker in an election expected to be held on Tuesday and that he believes he has enough votes.
"I wish Speaker Fox well," Majority Leader Nicholas Mattiello told The Associated Press. He said he was saddened by the situation but that legislators would now be able to "work together to move the House of Representatives and the state forward in a positive direction."
While questions remain about the nature of the investigation and Fox's role in it, his enduring legislative legacy is most likely to be legalizing gay marriage. In 2011, he abandoned a legalization push because of opposition in the Senate. Instead, he pushed civil unions. He was roundly criticized by some gay marriage supporters, who felt bitter and let down.
But just two years later, Fox was instrumental in pushing the legislation through as the political climate on the issue shifted nationally. He became emotional at the bill-signing ceremony on the Statehouse steps last year as he addressed the crowd and talked about his longtime partner, Marcus LaFond, whom he called "the love of my life."
"This tells me our relationship does matter," Fox said. "It means that we mean something."
The two were married last year in Fox's Statehouse office.
Rep. Frank Ferri, D-Warwick, recalled Fox's years as majority leader and said he was respected for his ability to cut to the heart of an issue during floor debates.
"I admire him. He's effective, thoughtful," said Ferri, a gay man and leading advocate for same-sex marriage in Rhode Island who clashed at times with Fox over how to handle the issue. "People would say, 'I didn't know where I was on an issue until he clarified it for me.'"
Fox is one of six children born to an Irish-American father and a Cape Verdean mother. His dad polished jewelry and worked odd jobs; his mom worked as a maid. In a 2011 interview with The Associated Press, he recalled the family moving into a new apartment with a view of the Statehouse and how he marveled at the dome.
His father had stressed the importance of education, but Fox was forced to drop out of Providence College when he died. "I felt defeated," he said in a 2010 commencement speech at Rhode Island College. "I was afraid that history was repeating itself."
Fox worked in a bank, scooped ice cream and sold vacuum cleaners. But he ultimately went back to school, enrolling at RIC — which he said "saved my life" — then attending Northeastern University School of Law on a full scholarship.
Fox in 2012 faced his toughest re-election campaign in years in part because of his support of a $75 million state loan guarantee for former Red Sox pitcher Curt Schilling's video game company, 38 Studios, which later went bankrupt. Earlier this year, he reached a settlement with the state ethics commission for failing to disclose more than $40,000 in legal work for a Providence economic development agency. Fox agreed to pay a $1,500 civil fine.
Associated Press writer David Klepper contributed to this report.