Exclusive

Former MMA star War Machine -- who is serving a life sentence for brutally beating his ex-GF -- got married behind bars ... and these aren't your typical wedding photos by a long stretch.

War Machine tied the knot with his longtime prison pen pal Ashley Farrington at Lovelock Correctional Center in Nevada ... taking a break from lockdown to say, "I do."

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.

As we reported ... War Machine was found guilty of sexual assault, battery by strangulation, coercion, kidnapping and several other charges after viciously attacking his ex, porn star, Christy Mack.

War is eligible for parole after 36 years when he's 71 ... so, the honeymoon will have to wait.