Former Rep. Jesse Jackson Jr. has agreed to plead guilty to violating federal campaign-finance laws in a deal with prosecutors, according to people familiar with the matter.

Mr. Jackson, an Illinois Democrat who resigned in November shortly after winning another term in the House, has signed paperwork agreeing to plead guilty, though a court hearing to enter the plea could be more than a week away, these people said. They said the sentence is likely to include some time in jail.

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