The man convicted in the murder of Drew Carey's ex-fiancee was just sentenced to spend the rest of his days behind bars ... more than 3 years after she fell to her death.

Gareth Pursehouse was sentenced to life in prison without the possibility of parole Wednesday after he was convicted of killing Dr. Amie Harwick ... where a jury found him guilty of first-degree murder with a special circumstance allegation after a trial in September.

Prosecutors alleged he broke into Harwick's home in February of 2020 and waited for her to return before attacking ... and ultimately threw her off a third-story balcony.

The prosecution said his crime stemmed from not being able to get over their prior relationship -- which had ended years ago. Interestingly, Harwick had apparently expressed fear to friends and confidantes over Pursehouse not long before she died.

Pursehouse's defense team acknowledged in court he had, in fact, illegally entered Harwick's house that night -- but argued that he never intended to kill her ... claiming Harwick might've climbed over the balcony herself and fell on her own, noting the prosecution hadn't definitively proven their client was the one who threw her off. Obviously, the jury disagreed.

TMZ broke the story ... Pursehouse was arrested quickly after Harwick's death, and investigators pinpointed him as the prime suspect with the help of surveillance video.