A pair of performers fall in love while working together, possibly even getting married and/or having kids over time. This happens quite a bit in Hollywood and is prime tabloid fodder. Such relationships seem to have a high breakup rate, but there are some long-lasting marriages that started this way.
What is actually being filmed is largely irrelevant. They're often a couple onscreen as well—when you spend all day pretending to be in love with someone, you may end up Becoming the Mask. However, it doesn't always happen that way. The point of the trope is that behind the scenes the two fall for each other.
The Muse is a Sub-Trope, which is about a male movie director falling in love with his lead actress. Cast Incest is another subtrope, namely the first type where the couple met while playing relatives, which adds a level of Squick before further thought reveals that it's no different from any other role.
In live theatre circles, the phenomenon is known as a "showmance" and tends to annoy their costars to no end. When it happens with a musical group, it's known as "bandcest", and while it tends to end badly, the fallout from the breakup often leads to the band's most famous work. Just ask Fleetwood Mac.
- Model Kate Upton and pitcher Justin Verlander began to date after meeting on the set of a commercial for the Major League Baseball 2K12 video game. They eventually married in late 2017, fittingly after Verlander helped the Astros win the World Series that year.
- Kenichi Suzumura and Maaya Sakamoto were first acquainted with each other when working on Mizuiro Jidai in 1996. In 2004, they were cast together as Shinn Asuka and Lunamaria Hawke, respectively, in Mobile Suit Gundam SEED Destiny. As the years went by, they seemed to constantly play love interests in a lot of titles they were cast in together, such as Zack Fair and Aerith Gainsborough, Mikiya and Shiki, and in a more one-sided case, Hikaru and Haruhi. Then in 2011, they got married.
- This happened between American voice actors Monica Rial and Matt Kelly while they were doing voice acting in Blue Seed. Monica was Momji and Matt was Kusanagi. They married after the voice dubbing was done. But they divorced shortly afterwards.
- Shinji and Asuka in the Advice and Trust Animated Actor omakes are just as in love with each other as their In-Universe counterparts (but without any of the codependency issues). Later omakes reveal that they got married in secret during a trip to Vegas.
- Happens In-Universe between Phineas and Isabella in Finding Dad while they sing a karaoke duet version of their one hit wonder Gitchee Gitchee Goo before having their first kiss.
- In the short story "Who Am I This Time?" by Kurt Vonnegut, the main character completely takes on the persona of whatever character he performs in the community play. A beautiful but socially awkward woman, when performing A Streetcar Named Desire with him, falls in passionate love with his persona. By living a life of Romance on the Set through various plays, they become Happily Married.
- In-Universe in Redshirts, Jenkins, whose wife had been Redshirted years before, sends a love letter to the actress who played her in Chronicles of the Intrepid when Dahl and the others go to the real world. In one of the epilogues, it is implied that she then ends up in a relationship with the actor who played him.
- In the commentary for The Tales of Beedle the Bard, Professor Dumbledore mentions the unfortunate casting choices in a theatrical version of the story The Fountain of Fair Fortune - the students playing "Amata" and "Sir Luckless" had been dating until "one hour before the curtain rose," at which point "Sir Luckless" dumped "Amata" for the girl who was playing "Asha." The two actresses began to duel and the resulting disaster is why Hogwarts no longer does school plays.
- French tenor Roberto Alagna and Romanian soprano Angela Gheorghiu are perhaps the most famous couple in the opera world after falling in love during a production of La Bohème in Covent Garden in 1994 and marrying 2 years later. In their 12-year on-off marriage, they have performed together onstage, done concerts and recorded albums together many times, making them a very famous couple in the opera world. However, in 2013, they've divorced for good.
- Italian soprano Mirella Freni married Bulgarian bass-baritone Nicolai Ghiaurov after frequently performing together. Their first performance together was a production of Faust in Genoa in 1961, and they married in 1978.
- American soprano Patricia Racette fell in love with American mezzo-soprano Beth Clayton during a production of La traviata in Santa Fe in 1997, and they married in 2005. They are currently the most famous lesbian couple in the opera world.
- American tenor Charles Castronovo met Russian soprano Ekaterina Siurina when they performed together in a production of L'elisir d'amore in Berlin and married in 2005. They've frequently performed together since then.
- Spanish soprano Montserrat Caballé married Spanish tenor Bernabé Martí in 1964 after they fell in love during a production of Madame Butterfly in A Coruña.
- African-American soprano Leontyne Price married African-American bass-baritone William Warfield during a European tour of Porgy and Bess, in which they performed together. However, they divorced in 1972.
- Russian soprano Anna Netrebko started a relationship with Yusif Eyvazov, an Azerbaijani tenor, during rehearsals of Puccini's Manon Lescaut in Rome. Within a year, the two got married.
- Olga Peretyatko, another Russian soprano, married Italian conductor Michele Mariotti after meeting him during a performance of Rossini's Beauty and Ironheart, which they both participated in.
- Bulgarian soprano Sonya Yoncheva married Venezuelan conductor Domingo Hindoyan after falling in love with him during an audition for Verdi's La traviata at the Berlin Staatsoper.
- Romanian soprano Virginia Zeani met Italian-Russian bass singer Nicola Rossi-Lemeni during performances of Bellini's I puritani in Florence of 1952. However, they met again during a production of Handel's Giulio Cesare at La Scala in 1956, and they married a year later.
- Spanish soprano Ainhoa Arteta married American baritone Dwayne Croft after they met a year before during a production of Fedora at the Metropolitan Opera.
- Lindsey Ellis (The Nostalgia Chick) and Todd Nathanson (Todd in the Shadows). In-universe, this has been translated to the Chick having an obsessive and completely unrequited interest in him, while he continues stalking Lupa.
- There have been several Channel Awesome couples, including Lupa and Phelous, and Nash and JO.
- Paul Schuler and Elisa Hansen (who plays Maven of the Eventide, Dr. Tease and the Makeover Fairy in the Nostalgia Chick's videos) got engaged on the 5th of November, 2012, and are now married with a baby boy named Grey.
- At least one couple in We Are All Pokémon Trainers have ended up in a relationship just like their characters.
- The French voices of Homer and Marge in The Simpsons (Veronique Augereau and Philippe Peythieu) got married in 2001.
- The voices of Kif Kroker and Amy Wong in the Latin American dub of Futurama are a married couple.
- Wayne Allwine and Russi Taylor, the voices of Mickey and Minnie Mouse, were Happily Married until Allwine's death.
- Slightly one-sided with Recess: Jason Davis, who played Mikey, had a crush on Ashley Johnson, who played Gretchen, when the show was on. In the show itself, there's no shipping.