Being Chief of Police, Martin takes the safety of Amity's residents very seriously, especially his children's safety. When he gets word that a young woman named Chrissie Watkins was killed by a shark, he immediately proceeds to close the beaches, before being stopped by Amity's mayor, Larry Vaughn, who cares about the town's economy and business. He is also very persuasive; when Mayor Vaughn is devastated after learning the shark problem hadn't been resolved yet after all, Martin urges him to hire Bartholomew Quint to take care of the threat. After hearing about a boating accident and finding a dead killer whale with huge bite wounds, Martin, fearing another great white shark is causing trouble around Amity Island, firmly prohibits his son Michael from going sailing for his safety; this causes Mike to resent his dad, but he later realizes that his father was only trying to protect him when he, his friends, and his brother Sean, are attacked by the great white.
Shortly after waking up, Martin gets a call about Chrissie Watkins' disappearance and heads for South Beach where she was last seen. He is horrified when he finds her severed arm (which a group of crabs are feasting on), and looks out at the ocean with a feeling of dread. A few moments later, at his office, he gets a call from the medical examiner, who tells him that Chrissie was most likely killed in a shark attack. Martin immediately asks for a list of water activities planned for the day and goes to get some materials to make "Beach Closed" signs. When Mayor Larry Vaughn hears about the incident, he intervenes, stating that shark attacks have never happened around Amity Island before, and insists a boating accident was what killed Chrissie. Martin reluctantly goes with Larry's claim. However, the Chief's fears are confirmed when the shark strikes again, killing an 11-year-old boy named Alex Kintner. Chief Brody, seeing that the situation is starting to get serious, decides that it's time to take action; he plans to put the extra summer deputies on duty quickly, deploy shark spotters, and call in a shark specialist. Martin spends the next few days studying and researching sharks.
Later, he meets with Matt Hooper, the shark specialist called in from the Oceanographic Insititute, and takes him to examine Chrissie's remains; Matt confirms that the cause of death was indeed a shark attack. Meanwhile, the local fishermen have just caught a tiger shark, leading Mayor Vaughn, Chief Brody, and everyone else to believe the threat is over. However, Matt isn't so sure it is the same predator, and suggests cutting it open to see what it recently ate; Larry objects, and Mrs. Kintner confronts the Chief, berating him for her son's death. That evening, Matt comes over to the Brody's house to meet with Martin and his wife, Ellen, and expresses his beliefs that the recently-caught tiger shark isn't the shark that killed Chrissie Watkins or Alex Kintner. He and Martin then go to cut the tiger shark's stomach open, and find no human remains. Martin knows he has tell the mayor; Matt tells him that is the least of his concerns, and what's more of a concern is that an even bigger shark is still out there.
Martin and Matt go out searching for the shark, and come across local fisherman Ben Gardner's boat, which has been severely damaged. Matt goes to examine the boat's hull and finds a great white shark's tooth embedded in it, but panics and drops it after finding Ben's remains. The next day, the two of them tell Larry that a monstrous great white shark is the real culprit, and that if he allows people to go swimming at the beaches, he will just put them in danger, but he dismisses their warnings and refuses to close the beaches, only allowing extra security. As expected, the shark turns up again and kills a boater, shocking Martin's son, Michael. Chief Brody persuades Mayor Vaughn, devastated by what happened, to hire Quint.
Quint, Matt, and Martin set out on Quint's boat, the Orca, to track down the shark, eventually coming face-to-face with the creature. Unfortunately, the animal escapes, and they have no choice but to wait for it to return. The shark reappears later, at night, and damages the boat. In the morning, Martin tries to contact the coast guard, but Quint breaks the radio, much to the Chief's fury. After chasing the shark, Martin suggests luring the shark towards shore. Unfortunately, Quint wrecks the engine, disabling the boat. Matt then attempts to poison the shark from the safety of a shark cage, without success; shortly afterwards, the shark leaps onto the boat and devours Quint, before going after Martin, who stuffs an air tank into its mouth, and shoots it, causing an explosion that kills the beast. Matt, having hid in a coral reef, surfaces, and he and Martin use the Orca's remains as a raft to get back to Amity Island.
Martin first appears driving to a grand opening party as a new hotel has been established on Amity Island. A little later, Deputy Jeff Hendricks comes into his office with an abandoned divers' camera, and shortly afterwards, he is informed of a boating accident, leading him to believe something isn't right. When his son Michael and his friends come across a killer whale carcass, Chief Brody worries that another great white shark may be behind the recent events, and privately tells Mayor Larry Vaughn about his concerns; he dismisses them and asks Martin not to press it this time.
While driving along the beach, Martin finds the remains of the boat that the two waterskiers used. Wading over to retrieve it, he finds the driver's burnt corpse. Later, at his office, he believes the divers' camera may provide clues as to what became of them. Going home, he prohibits Mike from sailing and gets him a summer job. The next day, at the beach, he mistakes a school of bluefish for a shark and unintentionally causes a panic, disgracing himself in front of everyone. That evening, he gets a call from Phil Fogarty, who has just developed the pictures from the camera, and watches as a close-up photo of the shark is developed. He immediately presents it to Larry and the town council, including Len Peterson, whom his wife works for; the town council disputes the proof and fires Martin for his actions on the beach, making Hendricks the new police chief.
The next day, Martin and Ellen, unaware that their children Michael and Sean are out sailing, prepare to go to the police department so Martin can return his police gear. Along the way, they see an ambulance heading to the docks, and follow it. They find diving instructor Tom Andrews being put on a stretcher. His team believes he was scared by something. Hendricks lets it slip that Michael and his friends have gone out sailing; Martin, knowing Michael and the others are in great danger, takes the police boat to find them, despite Hendricks' protests. Along the way, he sends for a helicopter to find them. They soon run into Tina Wilcox, who had just witnessed her boyfriend Eddie Marchand get eaten by the shark, and confirms the Chief's fears. Martin signals a nearby boat to transport Ellen, Hendricks, and Tina back to shore while he continues searching.
Meanwhile, Michael, his brother Sean, and the others are attacked by the shark. Two of Mike's friends, Timmy and Polo manage to save him and leave to find help. The helicopter that Martin requested soon arrives. Unfortunately, the shark destroys it and kills the pilot before knocking Sean in the water and killing Marge as she gets him to safety. Martin eventually encounters Mike, who tells him Sean is out there, much to his shock, and Timmy and Polo give him their whereabouts. Martin instructs the three of them to get to safety as Mike apologizes for not knowing about the shark before continuing on. He finally locates them at Cable Junction, a small island that provides electricity to Amity Island, but the shark startles Martin and causes him to maroon the police boat on Cable Junction. He tries to use a winch to pull them, but hooks a power cable. After the shark knocks everyone except for Sean and Jackie Peters in the water, Martin produces an inflatable raft, and smacks the power cable with an oar to attract the shark and gets it to bite the cable, resulting the shark being electrocuted to death. With the shark gone, Martin collects Sean and Jackie and they join the others on Cable Junction.