It's said DiCaprio will play an aging, out-of-work actor in the film.
The pair previously worked together on the phenomenally popular, The Wolf of Wall Street.
The last time Leonardo and the two-time Oscar victor collaborated was in 2012 on Tarantino's critically-acclaimed western, which amassed $425.4M at the worldwide box office.
Sony then picked up the rights for the feature film back in November, following a heated bidding war.
The yet-unnamed film, already slated for release on August 9, 2019, will center around cult leader and convicted murderer Charles Manson.
Deadline confirms the rumors that Tarantino has reached out to Margot Robbie to play Tate. Should DiCaprio join the project, it will be his first film since starring in 2015's "The Revenant" directed by Alejandro Gonzalez Inarritu which earned him a Best Actor award at the 2016 Oscars.
Plot details for the unnamed Manson film are still thin on the ground at this stage, but it's thought to be a 1969-set ensemble flick that in some way details the Manson family murders - which were orchestrated by Charles Manson, one of the most widely-known serial killers of all time.