Dubois, 22, put Dutchman Snijders down three times in the first round with brutal body shots.
A fourth knockdown early in the second round saw the referee end the contest.
The behind-closed-doors bout at the BT Sport studios was the Londoner’s first fight since December and extends his record to 15-0.
“It was a foregone conclusion I was going to win,” said Dubois. “It was just about getting the ball rolling again.”
Dubois and Joyce, 34, will fight at London’s O2 Arena on 24 October after their highly anticipated bout was rearranged.
Dubois said he will be “more than ready” for Joyce, adding: “I’m 100 per cent sure that it’s going to be a great fight but I’ll win. I’m excited about that.”
The pair were due to meet on 11 July but the coronavirus pandemic forced a change of date.
Promoter Frank Warren expects the winner will be “nailed on” for a world-title shot.