The armorer who put a live round into the gun that Alec Baldwin was rehearsing with on the set of the film “Rust” in 2021 when it went off, killing the cinematographer, was found guilty of involuntary manslaughter on Wednesday.

The conviction of the armorer, Hannah Gutierrez-Reed, marks the first time a jury has weighed in at trial on the fatal shooting of the cinematographer, Halyna Hutchins.

The top charge carries a penalty of up to 18 months in prison.

After the verdict was read, prosecutors asked that Ms. Gutierrez-Reed be taken into custody and the judge, Mary L. Marlowe Sommer, agreed.

A court officer led Ms. Gutierrez-Reed out of the courtroom, not in handcuffs.

Mr. Baldwin is also facing a charge of involuntary manslaughter and is scheduled to stand trial in July. He has argued that he was not responsible, since he was told that there were no live rounds in the gun and there were not supposed to be any on the set.

Ms. Gutierrez-Reed’s trial, which lasted two weeks at the First Judicial District Courthouse in Santa Fe, N.M., focused on the fact that Ms. Gutierrez-Reed was supposed to load Mr. Baldwin’s revolver that day with dummy rounds, inert cartridges that are meant to resemble real bullets on camera but which cannot be fired.

But one round turned out to be live. And when the gun went off as Mr. Baldwin worked with Ms. Hutchins to set up camera angles, it fired a bullet that killed her, wounded the movie’s director and left the movie industry wondering how it could have happened on a film set where live ammunition was supposed to be banned.