Catherine O'Hara Cause of Death Revealed

Catherine O'Hara passed away from a blood clot in the lungs ... TMZ has learned.

The L.A. County Department of Public Health released the actress' death certificate Monday, which lists her cause of death … O'Hara's immediate cause of death is listed as pulmonary embolism, with rectal cancer as the underlying cause.

The death certificate says she was cremated and her remains were given to her husband, Robert "Bo" Welch.

We broke the story ... O'Hara passed away at the end of January, two sources with direct knowledge told us at the time. She had been rushed to the hospital in serious condition. She was reported by dispatch personnel as having trouble breathing.

Catherine played numerous iconic characters over the years, starring in the likes of "Schitt's Creek," "Beetlejuice," and most famously playing Macaulay Culkin's mother in the first two 'Home Alone' movies.

She most recently earned an Emmy nomination for her work opposite Seth Rogen in the Apple TV+ series, "The Studio."

Along the way, she nabbed multiple award season wins -- including 2 Emmys, 2 SAGs and a Golden Globe among others.

Catherine was 71.