Morgan Creek Productions has been working for years to bring the late rapper's story to the big screen.
It is operating with a sense of urgency given that the music rights will revert back to Tupac's mother, Afeni Shakur, at the end of the year if the film is not in production by then, said The Hollywood Reporter.
Franklin was poised to direct as recently as the summer, picking up the baton after John Singleton dropped out in April and trashed Morgan Creek in the process.
In late October, producers Emmett/Furla filed a USD 10 million lawsuit against Morgan Creek, saying the company breached a co-production agreement by selecting a lead actor and setting a budget and production schedule without Emmett/Furla's approval.
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It was not the first time the project had become entangled in a lawsuit. The studio sued Afeni for the music rights to the film.
Given the success of another rap biopic, Universal's "Straight Outta Compton", a Tupac film was seen as particularly attractive.
The Tupac character has appeared twice in film, in 2009's "Notorious" and "Straight Outta Compton", both supporting roles played by Anthony Mackie and newcomer Marcc Rose, respectively.
Boom has previously directed two features, 2009 action comedy "Next Day Air" and the made-for-home-video action movie "SWAT: Firefight" - but has made a name for himself in the commercial and music scene.
He won video director of the year at the BET Awards for his work with artists such as Nicki Minaj, Lil Wayne and Meek Mill.