Along with the couple photo, Amanda initially shared a snap of her huge diamond ring. "Engaged to [the] love of my life," she captioned the post.
The Hairspray star is still under her parents’ conservatorship, so won't be able to get legally married without approval from a judge.
A source told The Blast that Bynes' family is aware of the engagement but no one has signed off on the marriage.
The website revealed that Paul is in his 20s and from the San Fernando Valley area of Los Angeles. His father is a prominent doctor in LA.
Amanda, who has struggled with bipolar disorder and addiction over the years, reportedly checked out of a sober living facility alone near the end of last year.
Until she finds her own place in Los Angeles, she decided to stay with her parents Lynn and Rick Bynes, according to an Entertainment Tonight insider.
Amanda’s history with substance abuse and brushes with the law are well documented.
The Easy A actress was charged with driving under the influence in 2012, and in 2013 she was caught smoking marijuana in the lobby of her New York apartment, she then threw her bong out the 36th-floor window when police were called.
That same year she started a fire in a stranger's driveway and was placed under psychiatric hold for 72 hours.
A year later she made - then took back - sexual abuse allegations against her father, Rick. She explained her decision to make the accusation: “The microchip in my brain made me say those things but he's the one that ordered them to microchip me.”