John Ratzenberger made his debut in the 1976 British-American comedy farce film ‘The Ritz’ directed by Richard Lester. The film saw mixed reviews upon release. The following year, he starred as ‘Sergeant Kopecki’ in the thriller film ‘Twilight's Last Gleaming’ directed by Robert Aldrich. The film received a lukewarm response from critics and was a commercial failure. That same year, he portrayed ‘Lt. James Megellas’ in the epic war film ‘A Bridge Too Far’ directed by Richard Attenborough. The film opened to mixed reviews and was a box office success. He continued to star in films like ‘Warlords of Atlantis’ (1978), ‘Superman’ (1978), ‘Hanover Street’ (1979), ‘Arabian Adventure’ (1979), ‘The Empire Strikes Back’ (1980), ‘Superman II’ (1980), ‘Outland’ (1981), The Good Soldier’ (1981), and ‘Gandhi’ (1982). In 1982, he joined the main cast of the American sitcom television series ‘Cheers’ created by Glen and Les Charles and James Burrows. He played the role of ‘Cliff Clavin’ and remained a part of the series until it went off-air in 1993.
In 1995, he voiced ‘Hamm’ in the American computer-animated film ‘Toy Story’ directed by John Lasseter. The film opened to critical acclaim and was a massive box office success, grossing over $373 million on a budget of $30 million. Ratzenberger continued to give his voice in films like ‘A Bug's Life’ (1998), ‘Toy Story 2’ (1999), ‘Monsters, Inc.’ (2001), ‘Spirited Away’ (2002), ‘Finding Nemo’ (2003), ‘The Incredibles’ (2004), ‘Cars’ (2006), ‘Ratatouille’ (2007), ‘WALL-E’ (2008), ‘Up’ (2009), ‘Toy Story 3’ (2010), and ‘Cars 2’ (2011). In 2012, he voiced the character ‘Gordon’ in the American computer-animated fantasy film ‘Brave’ directed by Mark Andrews and Brenda Chapman. The film was a major critical and commercial success. The following year, he voiced ‘Harland’ in the American 3D computer-animated sports comedy film ‘Planes.’ Even though the film saw negative reviews upon release, it managed to come out as a commercial success. He was next seen in ‘Planes: Fire & Rescue’ (2014), ‘Inside Out’ (2015), ‘Finding Dory’ (2016), ‘Cars 3’ (2017), ‘Incredibles 2’ (2018), ‘Toy Story 4’ (2019), and ‘Onward’ (2020).
Apart from films, Ratzenberger has also appeared in television series like ‘The Simpsons’ (1994, 2014), ‘Murphy Brown’ (1995), ‘Toy Story Treats’ (1996), ‘Happily Ever After: Fairy Tales for Every Child’ (1997), ‘That '70s Show’ (2001), ‘Frasier’ (2002), ‘8 Simple Rules’ (2003), ‘Made in America’ (2004-2008), ‘Drop Dead Diva’ (2012-2014), ‘Legit’ (2013, 2014), ‘Lego Star Wars: The Freemaker Adventures’ (2017), and ‘Just Roll with It’ (2020). In 2021, he joined the voice cast of the American computer-animated streaming television series ‘Monsters at Work.’ The second season of the series is currently under development.