The 28-year-old has been allowed to leave on compassionate grounds following the birth of his first child.
"Me and my wife, Jessica, have recently celebrated the birth of Grace, our first child, back home in Australia, and we have come to the extremely difficult decision of leaving behind my professional career as a Bradford player, in Super League," L'Estrange told the club's official website.
"I would like to thank Bradford Bulls for allowing me to be released from my contract. I have had an absolutely amazing time with the Bulls and I have played alongside some fantastic players."
L'Estrange spent four years at the club.