Brendan Dassey, a subject of the Netflix documentary series “Making a Murderer,” won a major court victory on Thursday, as a federal appeals court upheld an earlier ruling by a federal judge overturning his conviction. The ruling came 10 years after Mr. Dassey was convicted of sexually assaulting and killing a 25-year-old photographer.

In a 2-to-1 decision, a panel of the United States Court of Appeals for the Seventh Circuit said that it agreed with the ruling last August by William E. Duffin, a federal judge for the Eastern District of Wisconsin. The judge had found that Mr. Dassey was coerced into a confession in which he admitted that he assisted his uncle, Steven Avery, in sexually assaulting and killing the photographer, Teresa Halbach. Mr. Dassey later recanted the confession.

“In addition to failing to apply a totality of the circumstances analysis to the facts of this case, as required by the Supreme Court, the state court acted unreasonably when it determined that, given the totality of the circumstances, Dassey’s confession was voluntary,” Judge Ilana Rovner wrote for the majority in a 104-page opinion.

But the real-life drama continues for Mr. Dassey, 27. For now, he will remain in jail, pending the Wisconsin Department of Justice’s next move. It has indicated that it wants to appeal the panel’s decision.