Beginning with treasure hunter Brock Lovett (Bill Paxton) searching the Titanic wreck for the fabled necklace named the Heart of the Ocean, the Titanic movie features actual footage of the wreckage. After recovering a safe that was thought to belong to first-class passenger Caledon ‘Cal’ Hockley, played by Billy Zane, Lovett hopes to find the Heart of the Ocean contained within. He finds nothing but soggy bank statements and a sketch of a naked woman wearing the necklace, and Lovett believes that he has hit a dead end.
A woman by the name of Rose Calvert (Gloria Stuart) sees Lovett on the news and contacts him. Lovett is uninterested in what she has to say at first but becomes intrigued when she tells him that she is the woman in the drawing. After being flown in to tell her story, we learn that Rose Calvert was once Rose DeWitt Bukater and was a first-class passenger on the Titanic. She begins telling her experience on the doomed vessel.
The movie begins with drifter Jack Dawson (Leonardo DiCaprio) winning third-class tickets for the Titanic in a poker game. He and his friend Fabrizio catch the ship just as it is leaving. It also shows first-class passenger Rose DeWitt Bukater (Kate Winslett), her mother Ruth (Frances Fisher), and her fiance Cal Hockley. Rose is on the way to Philadelphia to marry Hockley, an arrangement made by her mother to protect her wealth status. Unhappy with this decision, Rose attempts to commit suicide by throwing herself from the Titanic.
She is confronted by Dawson, who convinces her to come up from the railing. Rose invites Jack to dinner as thanks, and after, Jack spirits her away to a third-class evening of dancing. Rose decides her future and asks Jack, an acclaimed artist to draw her nude wearing only the Heart of the Ocean.
The two then find their way to the cargo hold, and a rich man’s car is waiting for them. They make love in the back seat before the ship hits an iceberg.
As people begin boarding lifeboats, Jack is arrested and locked in the master at the arms office. Instead of boarding a lifeboat, Rose goes back to help Jack, and the two must fight for survival. Jack and Rose’s fiancé Cal finally convince her to board a lifeboat, and Cal assures her that he has arranged to get both men off the boat safely.
Cal double-crosses Jack, and Rose decides to return for him yet again despite her being urged to stay on the lifeboat. Rose finds Jack, and Cal chases them into the flooded first-class dining room with a pistol. Once they escape Cal, he returns the deck and boards a lifeboat after pretending to look after an abandoned child.
Rose and Jack go down with the ship, and Jack helps her onto a door that can support the weight of one person. While Jack is in the freezing water, they exchange loving words, and Jack dies of hypothermia. Once aboard the Carpathia, Rose gives her name as Rose Dawson. She sees Cal one more time frantically looking for her but hides her face in a blanket just as he looks in her direction. Rose then proceeds to do everything she and Jack promised to do together and lives her life.
Back on Lovett’s ship, Rose walks to the side, produces the Heart of the Ocean, and tosses it overboard. In the last scene, Rose is met by Jack on the grand staircase of the Titanic. They kiss and are applauded by those who were lost in the disaster. It isn’t known whether or not she is dreaming or if she dies (Jack told her she would die in her bed as an old woman), and James Cameron leaves this up to the viewer to decide.