Dashiell often gets into trouble and loves playing pranks on his least favorite teacher, Mr. Bernie Kropp. He believes that he should use his superpowers; his mother, Helen Parr/Elastigirl, disagrees. His goal is to compete in sports: his power of speed would make him special. His mother forbids it on account that "Everyone's special" (noted by Dash to be the equivalent of saying "No one is").
Dash's reckless nature and one-track mind always gets him into trouble with his big sister, Violet. In one scene, he teases her about her crush on her classmate, Anthony "Tony" Rydinger, which insults her. This erupts into a fight, in which Dash runs around the table, hitting Violet, and Violet retaliates by generating her force-field that Dash crashes into. The fight is broken up when Lucius Best/Frozone, a long-time family friend, rings the doorbell. Dash squirts water at Lucius for him to freeze it—a tradition between the two.
After Dash's father, Bob Parr/Mr. Incredible, returns from his night with Lucius, Dash and Violet hear their parents arguing loudly and rush into the scene to investigate. Bob feels the wind, which makes him sense Dash's presence in the same room he and Helen are, and assures the children that he and Helen work as a team, no matter what. Helen apologizes to the children for waking them up before ushering them back to bed. After Bob, returns from Nomanisan Island, father and son are seen playing numerous games including catch (this foreshadows a later event).
When Bob is captured by Syndrome on his return to Nomanisan Island, Helen packs her bags to rescue him after a brief visit with superhero fashion designer, Edna Mode. As she does, Dash sees the suit made for him and puts it on, naming himself The Dash. Dash then goes after his mother, wanting to find out what his mother is up to, with Violet following him, trying to stop him. The two siblings end up stowing away on a plane Helen has borrowed from a friend. When Helen finds them in the plane, the siblings argue on who's fault it is, and Helen is shocked that they have left Jack-Jack alone in their house, to which Violet replies that she got someone to take care of the baby. During the flight, missiles, sent by Syndrome, close in on the plane, making Dash worried about getting killed by the missiles. Helen is forced to save her children's lives by wrapping herself around Dash and Violet just as the missiles slam into the plane, destroying the aircraft. The three then fall from the sky, but Helen then grabs the two and turns her body into a parachute. Landing in the water, Dash despairs that he, Violet, and Helen are all going to die, but Helen sternly tells the two to get a grip; otherwise, she will ground them.
Seeing contrails left behind by the missiles, Helen decides to head in the direction where the missiles came from. She then changes into a lifeboat with Dash serving as the outboard motor, for which Helen praises him upon their arrival at a shore of Nomanisan Island. In their camp out (a cave), she warns the children that the bad guys they will be facing will be different from those on cartoons as those bad guys are merciless and will kill them if they got a chance. Thus, she encourages Dash to run as fast as he can should things go wrong, to his excitement at being allowed to use his powers, before she goes off to Syndrome's base.
Being rebellious, Dash hates it when Violet is in charge. He and Violet have another verbal disagreement, in which she is concerned Dash thinks this is merely a vacation. She then lets him know otherwise: "Mom and Dad's lives could be in danger, or worse, their marriage." Dash then decides to explore deep into the cave, but is forced to retreat when flames come in his direction (The cave Dash and Violet are in is actually a rocket exhaust pipe). Dash grabs Violet, and they narrowly escape the flames, just in time to see a rocket taking off into the night sky. They spend the rest of the night in a jungle, huddling together to keep warm.
The next morning, Dash hears a monitor robot (disguised as a wild bird) asking for identification. Their curiosity triggers a deafening alarm of the robotic bird, prompting them to run with the bird flying after them. Later, the two are cornered by three Velocipods that are patrolled by Syndrome's security guards. Dash, remembering his mother's advice, starts running at super-speed. Two of the security guards chase him (while the third engages an invisible Violet). In this episode, Dash discovers just how formidable his superpower really is: he has a superior reaction time, he can deliver rapid-fire punches (but lacks the strength to do any lasting damage), and at full speed he can run on water. At the end this "100 Mile Dash", he gets cornered by the two Velocipods. He stops on the lagoon's surface and immediately submerges, saving his life as his pursuers collide into each other.
Eventually, Dash returns to Point A just in time to save Violet from the third guard, ramming into him and knocking him down. Dash lands on the guard and punches him for trying to harm the former's sister, but the guard punches Dash off and threatens to shoot him. Seeing the danger her brother is in, Violet jumps in and encloses herself and Dash within her force-field to protect them from gunfire. She and Dash discover that she can float inside her force-field if she generates them in mid-air. Dash then proceeds to move the force sphere by running along its inside surface, propelling it at considerable speeds and mowing down everything in their path. After destroying a couple more Velocipods, they literally run over their parents. After a brief and joyful reunion, the family works as a super-team for the first time as another wave of henchmen find them and attack them. Dash runs around the family to create a dust cloud, from which the Incredibles attack the guards, taking them down one by one.
Just then, Syndrome arrives at the scene and immobilizes them in his zero-point energy. Imprisoning the family in his base's containment unit, Syndrome describes Operation Kronos: his plan to fraudulently become a superhero. Amidst Bob Parr's apology to Helen, Violet releases the restraints, allowing their escape. There are no jets in the hangar Helen saw during her arrival to Nomanisan Island, but Dash sees a rocket. Unfortunately, Helen has no knowledge on how to fly a rocket. Violet informs her to "just use the coordinates from the last launch." Syndrome's former co-worker Mirage, who has defected from her employer after folding her apparent relationship with him, steps in to help.
Helen holds a van to the rocket as Dash maintains his impatience asking, "Are we there yet?" Upon their landing, Dash and Violet are nearly crushed to death by Syndrome's Omnidroid v.10, but Bob holds up the robot for Helen to reach for the kids and take them to safety. Bob then finds a remote Syndrome has left behind. Violet and Dash notice that "the remote controls the robot," and Dash calls to his father to throw the remote. Bob then throws the remote to Dash, who crosses the pond while catching it (garnering amazement from his dad). After the family and Lucius finally secure the remote, Violet and Dash still childishly fight over it—during which Dash presses a button that frees Bob from the robot's claw it has fired at him—until Helen takes the remote. The Omnidroid is finally destroyed when Bob fires the detached claw that penetrates through its bulk and rips out its brainpan.
On their way home, Dash gets excited about how much fun he had during the entire adventure. When they arrive, they stop Syndrome from capturing Jack-Jack. Syndrome is killed when his cape gets snagged in the turbine of his manta jet, and Violet saves the family from being crushed by plane wreckage, which totals their home. Dash now wonders if they have to move again, to that the answer is yes. When the smoke clears, one of their neighbors, a tricycle-riding young boy named Rusty, is amazed by what happened as he yells, "That was totally wicked!"
A few months later, Dash finally gets his chance to participate in track & field, but agrees with his parents that he cannot do anything to compromise the secret of the Incredibles nor grant himself an unfair advantage over the other contestants. Dash restrains himself, running only fast enough to win a silver cup, to which his family congratulates him for. When celebrating Dash's athletic accomplishment, his victory is interrupted by a newly appeared super-villain, The Underminer, who emerges from underneath the earth. Dash and the rest of the family don their masks and suits, showing their rededication to fighting crime.