Jack and Rose - two complete opposites. Jack is a 3rd class artist who has no restrictions and does anything his heart desires. Rose is a rich, first class person who was raised to be what a prim and proper woman in 1912 should be. Yet, when these two meet each other, they find true love.
This all starts when Jack wins his ticket aboard the Titanic in a game of poker "A VERY lucky hand," as he put it. Rose, meanwhile, is boarding the Titanic grimly, engaged and going to the United States in order to be married to Cal Hockley, heir to Pittsburgh's Steel Fortune. She feels as though "[Titanic] was a slave ship, taking me back to America in chains."
One night, Rose decides she simply can't take the "endless parade of parties and cotillions, yachts and polo matches... always the same narrow people, the same mindless chatter. I felt like I was standing at a great precipice, with no one to pull me back, no one who cared... or even noticed," so she climbs over the railing of Titanic and is ready to jump. She finds someone will pull her back, though. Someone who does care. This person is Jack. She pushes him away, but replies with "I can't. I'm involved now. If you let go I have to jump in after you." With that, and a little more persuasion, he manages to get Rose back onto the ship. Cal finds them together, misjudging their meeting at first, but as he figures out what went on, decides to invite Jack to dinner.
The dinner goes better than Cal and Rose's mother Ruth had hoped. With Jack dressed in a tux loaned to him by the Unsinkable Molly Brown, and a few good words such as "See, my folks died in a fire when I was fifteen, and I've been on the road since. Somethin' like that teaches you to take life as it comes at you. To make each day count." After the dinner, Jack invites Rose to a "Real Party," which is in the 3rd class social room. Jack learns that Rose, as he can become a first class dining comrade, she can let her hair down and have some fun by dancing, drinking, and an occasional ballet move, resulting in a kind-of hug.
The next day, Jack "borrows" a topcoat and hat and goes to see Rose. He pours out his feelings to Rose, saying "Rose, you're no picnic. You're a spoiled little brat even. But underneath all of that you are the most amazingly wonderful girl...woman that I have ever known. I'm not an idiot. I know how the world works. I've got ten bucks in my pocket, I've got nothing to offer you and I know that. I understand. But I'm too involved now. You jump I jump remember?" Rose doesn't know what to do. She tells Jack to leave her alone.
Later, Rose goes to see Jack at the front of Titanic. There, he teaches her to "Fly," and they kiss as they realize that there is something between them. Something more than a man saving a woman. Something that can bring together these two people that are so different. Maybe even... Love?
Rose brings Jack to her first class suite. She shows him La Coeur de la Mer - The Heart of the Ocean. And she wants him "to draw me like one of your French Girls wearing this... wearing only this." He does, a bit shaken, and the drawing comes out beautifully. She places this into Cal's safe with a short note "Darling, Now you can keep us both locked in your safe. Rose." When Cal finds this, he is furious, and makes a plan.
After Jack and Rose spent a little time in a car, they return above deck, kissing. The fateful iceberg then hits the ship. They return to Rose's suite, not really realizing that the ship is doomed, and planning on telling Cal what has happened between the two of them, Cal then makes it look as though Jack stole the diamond "while [Rose] was putting her clothes back on." Jack is handcuffed and taken to the ship's jail, where Spicer Lovejoy, Cal's body guard, beats up Jack and leaves him handcuffed to a pipe in pain.
Rose, meanwhile, is confused. Before she can sort anything out, a crew member comes to their suite and tells them go get their life jackets on and stand with other first class passengers. As they are about to board a lifeboat, Ruth asks about the lifeboats being by class. Rose yells "Oh, mother, shut up! Don't you understand? The water is freezing and there aren't enough boats. Not enough by half. Half the people on this ship are going to die." "Not the better half," Cal remarks. Rose then realizes her stupidity in even thinking about a man like Cal. She then runs off to find the person she does care for, Jack.
Rose finds Jack in the flooded basement of the ship. She races to find a way to free him, but can't. She grabs and ax and rushes back. Jack asks Rose to "try a couple practice swings." and she hits the mark four inches away, he replies with "Okay, that's enough practice." Luckily, Rose hits her mark and Jack and her run to the boats. They are no longer accepting men. Rose refuses to get onto one without Jack. Cal promises her he and Jack will be able to get on a boat on the other side of the ship, which is, of course, a lie. She reluctantly boards.
As the lifeboat is being lowered, she looks back at Jack and sees a tear run down his cheek. She can't stand to be without him. She jumps up and back onto the Titanic. Jack turns and runs back down into the Titanic and down the Grand Staircase, where he finds Rose. "You jump, I jump, right?" Rose asks tearfully. They hug, and return to the upper deck. There are no more boats left, so they walk to the very end of the Titanic. As the ship is sinking, Rose says "Jack, this is where we first met!"
When the ship goes under, Jack and Rose swim up and try to find something to float on. They find a piece of wood, but only one can fit on it without tipping it over. Jack, knowing he will most likely die, gives the space to Rose. "I love you Jack," she says as she begins her good-byes. "No, don't do that. You must do me this honor. Promise me you'll survive. You must promise me that you won't give up. No matter what happens. Promise me now, promise," Jack says to her, shivering in the freezing water. "I promise." "And never let go of that promise." "I won't ever let go, Jack. I'll never let go."
Hours later, a boat comes to save people still alive in the water. Rose turns to Jack. He's asleep. Rose shakes him, but he doesn't wake up. She closes her eyes, realizing he's dead. She looses interest in the boat. She lies there with Jack's body, not wanting to live anymore. Then, she remembers her promise. She gets up and tries to call after the boat. She is too weak, though. Rose looks down at Jack and realizes her hand is frozen to his. She breathes on it, melting the ice, and lets go. She watches him sink into the ocean. "I won't let go. I promise," she says. Then, Rose gets into the water and grabs a whistle of a man nearby. She blows on it, and the boat comes and rescues her. When she arrives at New York, she lives under the name Rose Dawson.
Then the story comes back to present day. Rose, now 101, dies warm and peaceful in her bed. She then returns to the Titanic. She flies through the hallways to the Grande Staircase, where she finds Jack waiting for her at the top. You see that Rose is once again 17, and they share a kiss. And we see that the love between Jack and Rose has and will last forever.