He was considered for the role of Duckie in John Hughes' film Pretty in Pink (1986), but his first lead role was with Molly Ringwald in The Pick-up Artist (1987).

and went several times through drug treatment programs unsuccessfully, explaining in 1999 to a judge: "It's like I have a shotgun in my mouth, and I've got my finger on the trigger, and I like the taste of the gun metal." He explained his relapses by claiming to have been addicted to drugs since the age of eight, due to the fact that his father, also an addict previously, had been giving them to him.

In April 1996, Downey was arrested for possession of heroin, cocaine, and an unloaded .357 Magnum handgun while he was speeding down Sunset Boulevard.

Despite Downey's lawyer, John Stewart Holden, assembling for his client's 1999 defense the same team of lawyers that successfully defended O. Simpson during his criminal trial for murder, Downey was sentenced to a three-year prison term at the California Substance Abuse Treatment Facility and State Prison in Corcoran, California.

At the time of the 1999 arrest, all of Downey's film projects had wrapped and were close to release.

Downey was under the influence of a controlled substance and in possession of cocaine and Valium.

In April 2001, while he was on parole, a Los Angeles police officer found him wandering barefooted in Culver City, just outside Los Angeles.

He had a personal coach in order to help him imitate Chaplin's posture, and a way of carrying himself.

In 1993, he appeared in the films Heart and Souls with Alfre Woodard and Kyra Sedgwick and Short Cuts with Matthew Modine and Julianne Moore, along with a documentary that he wrote about the 1992 presidential campaigns titled The Last Party (1993).

He starred as the title character in the 1992 film Chaplin, which earned him a nomination for the Academy Award for Best Actor and won him the BAFTA Award for Best Actor in a Leading Role.

After being released in 2000 from the California Substance Abuse Treatment Facility and State Prison where he was on drug charges, Downey joined the cast of the TV series Ally Mc Beal playing Calista Flockhart's love interest. His character was written out when Downey was fired after two drug arrests in late 2000 and early 2001.

He had also been hired for voicing the devil on the NBC animated television series God, the Devil and Bob, but was fired when he failed to show up for rehearsals.