Aaron Hernandez, a former tight end with the New England Patriots, was convicted of first-degree murder and several weapons and ammunitions charges Wednesday, ending the stunning downfall of a player who was once one of the N.F.L.’s most promising young stars.

Mr. Hernandez, 25, will spend the rest of his life in prison without the possibility of parole for the murder of Odin Lloyd, who was dating the sister of Mr. Hernandez’s fiancée, Shayanna Jenkins. The body of Mr. Lloyd, a 27-year-old semiprofessional football player, was found, shot six times, in June 2013 in a pit at an industrial park near Mr. Hernandez’s home in North Attleboro, Mass.

Mr. Hernandez’s motive, prosecutors said, was that Mr. Lloyd spoke with people Mr. Hernandez did not like at a bar in Boston. Their case, which was largely circumstantial, took more than two months to present; more than 100 witnesses were called. No murder weapon was found, and no independent witness to the shooting came forward.

The defense’s case lasted only a day and included three witnesses. Mr. Hernandez’s lawyer, James Sultan, acknowledged that his client was at the scene of the killing and claimed that two other men, who are charged separately for the crime, committed it while high on PCP.