It is the capstone of a remarkable rise in the sport for Cameron, who has now gone 17 fights undefeated.
She won the WBC title back in 2020, added the IBF title last year and has finally managed to prove she is the best by adding the WBO and WBA championships by beating McCaskill.
"I've got faith in my team so I knew I'd get the win," Cameron, 31, told Dazn.
"I knew I was the better boxer but it's hard not to get into a scrap.
Despite her dominance at super-lightweight, this win was no forgone conclusion as McCaskill is the reigning undispute welterweight champion.
"It was the toughest opponent I've ever had," she admitted.
"She's undisputed at 147 [lb], I got the win unanimous so let's go again at 147 and I'll take those belts off her.
"I put my belts on the line so she can whack hers on the line and we'll go again."