In CCTV footage, the man is caught throwing the toddler into the pool, allowing her to take in gulps of swimming pool water in the process.
Throwing her in repeatedly, then leaving her to ingest water, the stepfather can also be seen attempting to hold the girl under the water for periods of time.
The tragic incident was caught on CCTV at a hotel in Morelia, south west Mexico, while the mother was reportedly sleeping in her room.
After being repeatedly hurled into the pool, the girl can be seen floundering in the water towards the end of the video, unable to keep her head above water.
As she sinks beneath the surface, the guardian can be seen half heartedly throwing a life ring at the three-year-old, though she is by this stage too weak to grab it.
The mum is said to have taken her daughter to hospital after realising the youngster had stopped breathing, where doctors confirmed she had died.
The man, who has not been named, has been arrested and charged with murder.