Robert F. Kennedy Jr. is expected to end his troubled independent presidential campaign on Friday, according to three people briefed on his plans, and has been in talks to throw his support behind former President Donald J. Trump.

Mr. Kennedy’s campaign said this week that he intended to address his “path forward” in a speech from Phoenix. Mr. Trump is expected to hold a rally later in the day in nearby Glendale, Ariz.

On Thursday, Mr. Kennedy filed paperwork to withdraw from the ballot in Arizona, a spokesman for the secretary of state’s office there said. It could not immediately be determined if the campaign was taking similar steps in other states.

But lawyers for Robert F. Kennedy Jr. also filed papers in federal court in New York on Thursday seeking to block the enforcement of a court decision that disqualified Mr. Kennedy from the state’s ballot. His lawyers also now seek to broaden a federal lawsuit he filed in May about his ballot application to argue that New York’s ballot requirements are unconstitutional.

The three people briefed on Mr. Kennedy’s plans emphasized that nothing was final, and that the iconoclastic Mr. Kennedy could still change his mind, but said that plans were in the works for him to appear alongside Mr. Trump on Friday. Some people close to Mr. Kennedy were still arguing forcefully against an endorsement, according to two of the people.

Mr. Kennedy’s backing of Mr. Trump would be the culmination of weeks of discussions, brokered by high-level intermediaries, between the two men, which began in July just before the Republican National Convention.