The actors could join the already cast Reese Witherspoon in the film based on the 2006 bestseller by Sara Gruen.
The plot features a circus employee love triangle set in Depression-era America.
Twilight star Pattinson would play a veterinary student who falls in love with the circus' equestrian rider (Reese). Penn is expected to take on the role of her husband, a dangerous animal trainer.
I Am Legend helmer Francis Lawrence has signed to direct.