Toaster was a good friend of Rob, the Master, who took pleasure in having her see his reflection in her silver faceplate and making faces as he waited for his toast to cook. After the Master left several years ago, Toaster was one of the few appliances in the house who never lost faith in the Master's eventual return.
One day, while Toaster and her four friends, Kirby, Lampy, Radio, and Blanky are cleaning the cottage, they see a man outside their window putting up a "For Sale" sign, leading them to believe that the Master would never return. Fed up and in denial that the Master would deliberately abandon them, Toaster declared that she and her friends would go out to find him. Despite initial reluctance, they eventually all agree, and set out into the wilderness. They come across many perils along the way, but Toaster retains her optimism and hope, even when all seemed lost.
Eventually, they are found by an appliance repair man after nearly drowning in a swamp. The repair man tries to dismantle Radio, but after scaring the repair man and rescuing Radio, they escape, making it to the apartment where the Master now lived. There, they are derided and thrown out by the Master's new appliances, who all believe themselves to be far more modern than Toaster and her friends. To make matters worse, they are hauled off to the junkyard to await disposal.
Unknown to Toaster and the other appliances however, the Master actually returned to the cottage, hoping to collect his favorite appliances for use in college. When he did not find them, he and his girlfriend Chris journeyed to the junkyard to dig up some spare appliances, since the Master did not love the modern appliances as he did his old ones. While there, he finds most of his appliances, who have been dodging an evil magnet crane determined to destroy them. The Giant Magnet nearly causes the Master to get crushed by the Crusher, but Toaster sacrifices herself by throwing herself into the gears, jamming them and stopping the Crusher, saving his Master's life. Upon returning home with all of his appliances, the Master fully repairs Toaster, and makes faces in his faceplate like he did as a kid. Toaster and her friends accompany their friend to college, happy to serve him once again.
Toaster is now living a happy life with the Master at his college, having become good friends with the animals the Master is caring for, along with the Dobermans working with the campus security. However, Toaster soon learns that the Master's thesis he was working on has been lost, and at the suggestion of Sebastian, they attempt to look for it on the computer in the clinic, learning about the Internet, before the computer is infected by a virus infecting the prototype TLW-728 supercomputer Wittgenstein, causing her to reveal that Sebastian and the other animals are to be shipped out to Tartarus Laboratories. Hoping to help both the animals and the Master, Toaster, aided by Radio, Blanky, Lampy, and Ratso, travel to the basement and meet Wittgenstein. Upon learning that he is down to his last tube, the extremely rare WFC-11-12-55 cathode tube, Toaster hopes they can help Wittgenstein, but an argument between Radio and Ratso regarding finding the tube in the college storage warehouse results in it being shattered, with blame being utterly pinned on Radio. When Wittgenstein learns from the clinic computer that the animals are about to be shipped out, he struggles to try and help, but the virus proves too much for him and he blows his last tube, seemingly killing him.
Toaster and the others are furious with Radio for dooming the animals and Wittgenstein, but as they cry and fear their friends are goners, Radio gives them a last chance as he sacrifices his own tube, also a WFC-11-12-55, to revive Wittgenstein to full health, destroying the virus and putting Wittgenstein back in his prime. With Wittgenstein's aid, Toaster and the others pursue Mack McCro and Jim Bob, and catch up to the truck before police and the Master arrive. Mack and Jim Bob are arrested, the animals are saved, and sometime later, Toaster watches while wearing the Master's graduation cap as the Master proposes to Chris and she accepts, and Chris provides a new WFC-11-12-55 to revive Radio that was found in Nome, Alaska.
With the animals all getting good homes, and Ratso coming with Toaster, his friends, the Master, and the new Mistress, the gang set off for their new life together.
Sometime following the Master graduating from college and marrying Chris, Toaster and the others are at their new home as the Master and Mistress return, revealing them to be the proud parents of a new baby boy, whom Toaster and the other appliances warm up to, dubbing him the "Little Master". However, one night, Toaster and the appliances pursue the Hearing Aid to the attic, only for the Little Master to have followed him as well, resulting in where the Little Master is apparently abducted. Interrogating the Hearing Aid, they learn that the Little Master has been taken to Mars. Contacting Wittgenstein for help, he provides all the details they will need to travel to Mars and rescue the Little Master. After running into some balloons that have been floating through space for who knows how long, Toaster and the others crash land on Mars. The first things they encounter are the satellite Viking 1 and an ACAM Christmas tree topper named Tinselina that had been placed inside Viking 1 back on Earth before he was launched to Mars. Soon, Toaster and the others run into an army of appliances known as the Wonder Luxe Appliances. They are seeking revenge on Earth for their company having built them to be defective, then being used as extra weight for rocket launches. Toaster and the others are soon brought before the leader of the Wonder Luxe Appliances, the Supreme Commander, a very large refrigerator, who refuses to change his mind to take vengeance on Earth. To that end, Toaster decides to run against him for leadership of the Wonder Luxe Appliances. During all this, Blanky reunites with the Little Master, and the Little Master makes physical contact with the Supreme Commander, causing him to temporarily change color and apparently warm up to him before reverting back to his normal appearance and behavior and blow him away, though leaving him rethinking his decision to destroy Earth.
Toaster ends up winning the election by a landslide, and as a result, the former Supreme Commander allows Toaster and the others inside him to reveal his true self to be the twin brother of the Hearing Aid, who had been separated from him for several decades. Thanks to the Little Master, Hearing Aid's brother decided to call off his attack, and agrees to come home with them, along with Tinselina. However, as they leave Mars and are seen off by the Wonder Luxe Appliances, Viking 1, and the other satellites, the Hearing Aid's brother realizes he forgot to cancel the countdown on the missile, as it is still set to launch and destroy Earth. Toaster bravely leaves the basket with Hearing Aid's brother to stop the missile, managing to deactivate it just as it was about to launch, leaving it to fall apart on the launch pad. After being picked up by the others, Tinselina sacrifices her hair and clothes to provide the organic fuel they need to return to Earth. They make it home just as the Baby Monitor, which Ratso had been subduing until they returned, breaks free of its restraints and wakes up the Master and Mistress. However, they come down to find the Little Master all right, and are unaware of their son's little adventure into space.
Sometime later, the family is celebrating Christmas, and when Rob and Chris notice Robbie wanting to say something, the first word out of his mouth is "Toaster", much to their confusion, before Robbie retrieves Toaster and the other appliances so they can enjoy Christmas with him and his parents. Once the Master and Mistress are out of the room, Toaster and the others look up at Tinselina, now having been given new clothes and hair, and sitting proudly on top of the Christmas tree.
- In the Timon & Pumbaa series, during Timon and Pumbaa's music video of "Stand by Me", a toaster that resembles the Toaster is seen.
- There is a cameo of Toaster and his friends in the series The Oz Kids, in the episode "Christmas in Oz".
- According to the original novella, Toaster is a Sunbeam.
- Despite Toaster being referred to as "he" in the movies, his voice actress Deanna Oliver and the first film's director Jerry Rees view Toaster as female. However, Thomas M. Disch simply refers to Toaster as "it".