Brock Lovett is heading up a crew of people searching for some kind of treasure in the wreck of the legendary Titanic. They find a case, thinking that the things they want are in it, but it's empty. However they do find a drawing of a woman apparently wearing what he's looking for: a very large diamond. An old woman sees him and gives him a call because she's the woman in that drawing. The old woman is Rose, one of the first class passengers. At first Brock is not interested in what Rose says, but when she tells him that she's the one in the drawing Brock is convinced.
She start telling the story where Jack Dawson won third class tickets for the Titanic in a poker game. He is with his friend Fabrizio. Rose is with her mother and her fiancee Cal - her mother arranged the marriage to protect her status and wealth. Unhappy with this decision, Rose attempts to commit suicide by throwing herself into the ocean. She is confronted by Dawson, who convinces her to come up from the railing. Rose invites Jack to dinner as a thanks, and afterwards Jack spirits her away to a third class evening of dancing. Rose decides to decide her own future and asks Jack, who is 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 find a rich man's car waiting for them. They proceed to make love in the back seat before the ship hits an iceberg.
As people begin boarding lifeboats, Jack is arrested, accused of stealing the Heart of the Ocean necklace, and is locked in the master at arms' office. Instead of boarding a lifeboat, Rose goes back to help Jack, using an axe to chop the handcuffs apart. Cal finally convinces her to board a lifeboat, and assuring her that he has made arrangements to get both men off the boat safely. Rose jumps from the boat because she can't stay there while Jack is suffering: 'you jump, I jump' staying on her mind. Cal shoots at both of them but misses. Both escape the shipwreck alive, and end up in the water. Jack helps her onto a door that can only support the weight of one person.
While Jack is in the freezing water, they exchange loving words, and Jack dies. Rose gives her name as Rose Dawson to hide from her mother and Cal. 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 that her and Jack promised to do together, and lives her life. When she's done telling the story she goes to the side of the ship and she drops the diamond into the water. In her dream, or possibly in death, she is with Jack standing at the staircase of the Titanic while waiting for her. They both kiss and are applauded by those who were lost in the disaster.