An appeals panel on Thursday vacated the conviction of Adnan Syed, whose case was chronicled in the first season of the hit podcast “Serial,” and ruled that he should be granted a new trial on all charges.

Mr. Syed was convicted in 2000 of the first-degree murder and kidnapping of his former girlfriend, Hae Min Lee.

In the ruling, the Maryland Court of Special Appeals said he had received ineffective legal counsel at his trial because his original lawyer had failed to call a witness whose testimony, if believed, “would have made it impossible for Syed to have murdered Hae.”

“Accordingly, Syed’s murder conviction must be vacated, and because Syed’s convictions for kidnapping, robbery, and false imprisonment are predicated on his commission of Hae’s murder, these convictions must be vacated as well,” the panel wrote. “The instant case will be remanded for a new trial on all charges against Syed.”