The flamboyant lightweight sank in a rear naked choke to beat Leavitt before getting on the microphone and revealing that he received a call telling him of his friend's passing on Friday morning, five hours before he weighed in.
"There's a stigma in this world that men can't talk - listen, if you're a man, and you've got weight on your shoulders ... please speak to someone, speak to anyone," an emotional Pimblett told the crowd.
"Please, let's get rid of this stigma, and men - start talking," he added.
The 27-year-old, who has racked up three straight wins since joining the UFC, left the cage to the strains of 'You'll Never Walk Alone', a song synonymous with his favourite football club Liverpool, with the crowd singing along.
Leavitt gave Pimblett some serious problems in the first round, but in the second the Liverpudlian's strikes started to tell and a knee to the head dropped the American, allowing Pimblett to take his back and secure the finish.
It was the second explosive finish of a night that had its origins on Merseyside as earlier on the main card flyweight Liverpool's Molly 'Meatball' McCann (32) pulled off a signature spinning elbow to down Hannah Goldy (30) en route to a TKO victory.
Despite the emotion of those two wins, the evening finished on a low note as Briton Tom Aspinall (29) suffered a serious knee injury seconds into his heavyweight clash with Curtis Blaydes (31).
Aspinall landed a heavy leg kick before falling back into the centre of the octagon clutching his right knee, with the American awarded the win by TKO as his opponent could not continue.
