The Brit stopped his Australian opponent in the 10th round despite Quinlan’s brave effort.
Eubank Jr appeared under pressure during the opening exchanges, even though he was odds on favourite before the fight.
And Quinlan forced him to bend at the knees in round six, showing he was a worthy match.
Eubank Jr’s jabs were somewhat wild but he managed to regain control as the fight wore on.
In ITV Box Office’s first night of live boxing, Chris Eubank watched his son preserve much-needed energy in the tank.
And round nine really saw momentum swing back in Eubank Jr’s favour as the 27-year-old caught Quinlan with a number of heavy blows.
In the next round, referee Howard Foster decided enough was enough as Eubank Jr was landing uppercuts from distance.
The Hove-born fighter has now won 24 of his 25 fights and claimed the IBO super-middleweight title.
After the victory, Eubank Jr said: “Now I am a world champion, I have my ticket to challenge the rest of the super middleweights.
“I’m coming for everybody, Degale, I want the rest of those teeth. Of course I want Golovkin, Saunders…
“We have the platform, let’s get these fights going!
“I’m comfortable at both weights. I was in Dubai for three months, I was shadow boxing on yachts. I want everybody!”
Before agreeing the fight with Quinlan, a shwodown with Gennady Golovkin had been suggested, and Eubank Jr appears keen to get it sorted.
