Citing sources close to the investigation, the newspaper said prosecutors concluded they could not charge Rivera because of ambiguities in the state's campaign finance laws and the statute of limitations.
The Miami-Dade State Attorney's Office and the Florida Department of Law Enforcement spent 18 months investigating the Miami-area congressman.
Records released late Monday show the Department of Law Enforcement last year suspected Rivera of "possible criminal and ethical violations." The allegations ranged from campaign fraud to falsifying financial disclosure forms during his years as a state lawmaker, the newspaper said.
Rivera was not found to have broken the law by raising hundreds of thousands of dollars in secret donations for a campaign for an obscure post within the state Republican Party, the Herald said.
The state attorney's office was expected to issue a memo formally ending the probe, the Herald said.
The Department of Law Enforcement confirmed the agency had wound up its investigation. A spokesman for Miami-Dade State Attorney Katherine Fernandez Rundle declined to comment.
Rivera's campaign issued a statement saying he "at all times acted in compliance with both the letter and spirit of Florida and federal campaign finance laws and has timely and properly reported all personal income."
The campaign said the Law Enforcement Department was given information refuting "all of their false and unfounded allegations against Congressman Rivera."
"In essence, FDLE launched a fishing expedition that became a wild goose chase and which has now proven to be a discredited, unwarranted and politically-motivated witch-hunt resulting in Congressman Rivera's exoneration," the statement said. "FDLE's unprofessional waste of taxpayer dollars in this matter is shameful."
The Herald said Rivera remains under investigation by the FBI and the IRS over a $510,000 payment from a dog track to a company managed by Rivera's mother and godmother.