Martin was in a Riverside County, CA courtroom on Thursday ... where the same jury that convicted him in only 4 hours decided his punishment.
The jurors spared his life -- electing not to give him the death penalty. Instead, Martin will spend the rest of his life in prison.
The story surrounding the September 2015 murders is disturbing, to say the least.
Martin brutally beat and killed his 64-year-old dad, 58-year-old uncle, and a 62-year-old man the family had hired to install an alarm to protect them from Martin. Officials say Martin used a black baseball bat (with his name inscribed on it) to kill the men.
The former ballplayer fled the crime scene ... but was apprehended the next day following a police chase.