In the late 1930s, at an illegal private poker card game, a young street urchin witnesses the massacre of a group of mobsters named Shoulders, Stooge Viller, The Rodent, The Brow, and Little Face at the hands of Flattop Jones and Itchy, two of the hoods on the payroll of crime boss Alphonse "Big Boy" Caprice. Big Boy's crime syndicate is aggressively taking over small businesses in the city. Detective Dick Tracy catches the urchin (who calls himself "Kid") in an act of petty theft. After rescuing him from a ruthless host, Tracy temporarily adopts him with the help of his girlfriend, Tess Trueheart .
Meanwhile, Big Boy coerces club owner Lips Manlis into signing over the deed to Club Ritz. He then kills him with a cement overcoat and steals his girlfriend, the seductive and sultry singer, Breathless Mahoney. After Lips is reported missing, Tracy interrogates his three hired guns, Flattop, Itchy, and Mumbles, then goes to the club to arrest Big Boy for Lips' murder. Breathless is the only witness. Instead of providing testimony, she unsuccessfully attempts to seduce Tracy. Big Boy cannot be indicted and he is released from jail. His next move is to try to bring other criminals, including Spuds Spaldoni, Pruneface, Influence, Ribs Mocco, Mumbles, and Numbers, together under his leadership. Spaldoni refuses and meets an untimely demise upon exiting(via a car bomb), leaving Tracy, who discovered the meeting and was attempting to spy on it, wondering is going on. Next day, Big Boy and his henchmen kidnap Tracy to attempt to bribe him and nearly kill him after he refuses by tying him next to a boiler rigged to explode, but he is saved by Kid.
Tracy tries again to get the testimony from Breathless he needs to put Big Boy away. She agrees to testify only if Tracy agrees to give in to her advances. He resists, despite his growing attraction. Tracy leads a seemingly unsuccessful raid on Club Ritz, but it's actually a diversion so officer Bug Bailey can enter the building to operate a secretly installed listening device so the police can hear in on Big Boy's criminal activities. The resultant raids all but wipe out his criminal empire. Unfortunately, He discovers Bug and captures him for a trap planned by Influence and Pruneface to kill Tracy in the warehouse. In the resulting gun battle, a figure with no face (known as "The Blank") steps out of the shadows to save Tracy after he is cornered and kills Pruneface. Influence escapes as Tracy rescues Bug from the same fate given to Lips Manlis, and Big Boy is enraged upon hearing that The Blank foiled the hit. Meanwhile, Breathless shows up at Tracy's apartment, once again in an attempt to seduce him. Tracy shows he is only human by allowing her to kiss him. Tess witnesses this and leaves town. She eventually has a change of heart, but before she can tell Tracy, she is kidnapped by The Blank. Tracy falls victim to another trap. He is drugged by The Blank and framed for the murder of corrupt District Attorney John Fletcher.
Big Boy is back in business, but he, too, is framed, in this case for Tess' kidnapping. Sprung from jail by his colleagues on New Year's Eve, Tracy sets out to save his true love with the help of Kid, who now renamed himself as Dick Tracy, Jr.. He arrives at a shootout outside Big Boy's club where most of Big Boy's men are gunned down by the police and Tracy himself (only Mumbles and 88 Keys, Breathless' piano player, survive to be arrested). Escaping through tunnels to a drawbridge out of the city, Big Boy ends up trapped with the bridge up, so he ties Tess to the mechanisms, but he is confronted by both The Blank and Tracy, who orders the latter to kill the crime boss. Desperate to escape, he shoots The Blank. Enraged, Tracy knocks Big Boy and sends him falling to his death towards the drawbridge's gears. Dick Jr. frees Tess and proceeds to learn The Blank's identity: beneath his mask, Tracy is shocked to find Breathless Mahoney, who tells him her attempt to control the city, and kisses him with her last breath. With the truth brought out, his name is cleared from the murder of Fletcher. Later, in the middle of a marriage proposal to Tess, Tracy is interrupted by a robbery in progress, and takes off with Dick Jr. But Tess puts the ring on before they leave.
- Warren Beatty as Dick Tracy: Square-jawed detective sporting a yellow overcoat and fedora. He is heavily committed to break the organized crime that infests in the city. In addition, Tracy is in line to become the chief of police, which he scorns as a "desk job".
- Al Pacino as Alphonse "Big Boy" Caprice: The main antagonist and the leading crime boss of the city. Although he is involved with numerous criminal activities, they remain unproven, as Tracy has never been able to catch him in the act or find a witness to testify.
- Madonna as Breathless Mahoney: An entertainer at Club Ritz who is interested in stealing Tracy from his girlfriend. She is also the sole witness to several of Caprice's crimes and is eventually revealed to be The Blank.
- Glenne Headly as Tess Trueheart: Tracy's girlfriend. She tries to convince him to enjoy life, as well as marry her.
- Charlie Korsmo as Kid: A scrawny street orphan who survives by eating out of garbage cans. He falls into the life of both Tracy and Trueheart and becomes an ally.
- Seymour Cassel and James Keane as Sam Catchem and Pat Patton: Tracy's two closest associates.
- Michael J. Pollard as Bug Bailey: A surveillance expert.
- Charles Durning as Chief Brandon: The kindly chief of police, who supports Tracy's crusade.
- Kathy Bates as Mrs. Green: The police department's stenographer.
- Dick Van Dyke as District Attorney John Fletcher: A city official who does the bidding of Big Boy, as a victim of extortion. He was gunned down by Mahoney who was using her Blank identity to frame Tracy.
- Dustin Hoffman as Mumbles: Big Boy's fast-talking henchman.
- William Forsythe as Flattop Jones: Big Boy's top hitman. His most distinguishing feature is his square, flat cranium and matching haircut.
- Ed O'Ross as Itchy: Another of Big Boy's henchman who suffers from an irritating skin condition.
- James Tolkan as Numbers: Big Boy's accountant.
- Mandy Patinkin as 88 Keys: A piano player at Club Ritz who becomes The Blank's minion.
- R. G. Armstrong as Pruneface: A deformed crime boss who becomes one of Big Boy's minions. He is very obsessed with killing Tracy, but he gets shot to death in his warehouse's trap by The Blank.
- Henry Silva as Influence: Pruneface's sinister top gunman.
- Chuck Hicks as The Brow: Big Boy's minion with 4 lumps on his forehead, giving him said name.
- Paul Sorvino as Lips Manlis: The original owner of Club Ritz and Big Boy's original mentor.
- James Caan as Spuds Spaldoni: A crime boss who refuses to submit to Big Boy, and dies in a car bomb explosion.
- Catherine O'Hara as Texie Garcia: A female crime boss who accepts Big Boy's dominance.
Hamilton Camp appears as a store owner. Allen Garfield, John Schuck, and Charles Fleischer make cameos as reporters. Walker Edmiston, John Moschitta, Jr., and Neil Ross provide the voices of each radio announcer.
- This movie was released in theaters with the Roger Rabbit short, Roller Coaster Rabbit.
- According to a trailer, this film was originally going to be released by Walt Disney Pictures. This likely happened before it got its rating, because the final version was released by Touchstone Pictures.