The convicted woman-beater slid a gold band on his new wife's finger -- the ring belonged to Ashley's grandmother. Hard to imagine this is what grandma had in mind.
Ashley's son and another family member were on hand for the nuptials ... and War Machine's best man was a guy named Mario Lino.
No wedding cake ... after all, you know what people put in prison cakes, right???
We're told the whole thing lasted 4 hours and was NOT conjugal.
TMZ broke the story ... War Machine proposed to his pen pal in early 2018 by reading her a love poem. He got down on bended knee, asking her to marry him even though he had no ring ... and she said yes.