The Lancaster County Coroner’s Office tells TMZ ... Mindler's manner of death has been ruled suicide, but the cause of death is still pending toxicology results.

We broke the story ... Matthew's college, Millersville University in Pennsylvania, confirmed his death with an announcement to the student body Saturday. It said he was found deceased that morning in Manor Township near the campus.

The first-year student had not been seen since Tuesday night after failing to return to his dorm room, and was reported missing late Wednesday.

Along with his role in "Our Idiot Brother" alongside Paul Rudd, Mindler also appeared in a sketch on "Last Week Tonight with John Oliver" in 2015 and had a few other acting credits to his name.

He was 19.