The first season of the American television series Loki, based on Marvel Comics featuring the character of the same name, sees Loki brought to the mysterious Time Variance Authority (TVA) after stealing the Tesseract during the events of Avengers: Endgame (2019), and is forced to help catch a dangerous variant version of himself. It is set in the Marvel Cinematic Universe (MCU), sharing continuity with the films and television series of the franchise. The season was produced by Marvel Studios, with Michael Waldron serving as head writer and Kate Herron directing.

Tom Hiddleston reprises his role as Loki from the film series, with Gugu Mbatha-Raw, Wunmi Mosaku, Eugene Cordero, Tara Strong, Owen Wilson, Sophia Di Martino, Sasha Lane, Jack Veal, DeObia Oparei, Richard E. Grant, and Jonathan Majors also starring. Loki was officially confirmed among the various Disney+ series in development from Marvel Studios in November 2018, along with Hiddleston's involvement. Filming began in February 2020 in Atlanta, Georgia, but was halted in March due to the COVID-19 pandemic. Production resumed that September and completed in December. The series takes place after the events of the film Avengers: Endgame, in which an alternate version of Loki created a new timeline, diverging from the events of The Avengers (2012). The season has a crime thriller tone, and sets up the events of the MCU films Doctor Strange in the Multiverse of Madness (2022) and Ant-Man and the Wasp: Quantumania (2023).

The first season premiered on Disney+ on June 9, 2021, running for six episodes until July 14, as part of Phase Four of the MCU. It received positive reviews, with praise for the cast's performances, musical score, and visuals. A second season was announced in July 2021.

Neil Ellice recurs in the season as TVA Hunter D-90, while Jaimie Alexander and Chris Hemsworth have uncredited appearances as Sif and the voice of Throg, respectively.

In November 2018, Disney CEO Bob Iger confirmed that a series centered on Loki was in development for Disney+ from Marvel Studios and that Tom Hiddleston was expected to reprise his role from the Marvel Cinematic Universe (MCU) films. Michael Waldron was hired as head writer and executive producer of the series in February 2019, and was also set to write the first episode. Waldron felt the series was an opportunity for "chaos and fun", such as connecting Loki to the story of D. B. Cooper, and his pitch to Marvel was to create a "big, crazy, fun time adventure" that would explore a new corner of the MCU and do something unexpected in each episode that would "blow up" the audience's ideas of what the series is.Waldron had assumed the audience was expecting the show to be similar to Quantum Leap (1989–1993), with Loki influencing historical events. Kate Herron, a fan of Loki, prepared a 60-page document for her pitch to be the series' director, feeling that a display of passion for the character would differentiate her from more experienced directors who were being considered. After developing her pitch during several interviews over Zoom with Marvel Studios executives Kevin R. Wright and Stephen Broussard, the London-based Herron was flown to Burbank for a meeting with top executives including Feige, Victoria Alonso, and Louis D'Esposito. Wright believed Herron's pitch had a "complete vision" of how to take the ideas for the series and turn them into something "wholly unique" to the MCU. In August 2019, Feige met with Herron in London to offer her the job as director for the series. Within 48 hours, she flew to New York to meet Hiddleston and discuss the character with him, and then went on to Disney's D23 Expo event, where she was announced as director and executive producer. Part of Herron's agreement to join the series was ensuring there was gender parity amongst the crew, particularly with the department heads. Daniel Kwan and Daniel Scheinert had also been approached to direct the season, but opted to pursue their own film project, Everything Everywhere All at Once (2022), which also dealt with multiversal concepts.

After Waldron signed on to write the MCU film Doctor Strange in the Multiverse of Madness (2022) in February 2020, writer Eric Martin was promoted to handle the day-to-day needs of the series, including being the lead writer on set, with Waldron and Martin later collaborating on any rewrites for the series. The first season consists of six 40- to 50-minute episodes, equaling 280 minutes total. In addition to Waldron and Herron, executive producers for the series include Feige, D'Esposito, Alonso, Broussard, and Hiddleston. The season sees an alternate version of Loki brought to the mysterious Time Variance Authority (TVA) to help fix the timeline and stop a greater threat, ending up trapped in a crime thriller of his own making, traveling through time and altering human history.

Elissa Karasik, Bisha K. Ali, Eric Martin, and Tom Kauffman served as writers for the season, with Jess Dweck also assisting, working for 20 weeks to create the season's scripts. Waldron found this period challenging because he also had to write the pilot episode, which is normally done in a separate development period before additional writers are hired, to establish the world of the series while conceiving story elements for the rest of the episodes. The basic structure of the season was determined in the first three weeks of work, knowing the first episode would see Loki interrogated, the second having "the police work" with Mobius M. Mobius, the third would see Loki and his female variant Sylvie on Lamentis, the fourth had "the conspiracy coming undone", the fifth would take place in the Void or "some form of it", and the final episode would be at the Citadel at the End of Time.

The season takes place after Avengers: Endgame (2019), which saw Loki steal the Tesseract during the 2012 events of The Avengers (2012) and unwittingly create an alternate timeline from the main MCU films. In the season, this "time variant" of Loki travels through time and alters human history, with the season exploring the questions "Where did Loki go after he picked up the Tesseract? Could Loki ever make a friend? [W]ill the sun ever shine on him again?". Exploring alternate timelines and the multiverse allowed Loki to introduce versions of other MCU characters in addition to other versions of Loki. Waldron also hoped to explore more complex character questions, such as what makes a person "truly good or truly bad", and what makes a hero, a hero, or a villain, a villain. He added that the season's setting in an alternate timeline meant it did not have to deal with the "immediate grief and aftermath" of Endgame and could instead "blaze a little bit of a new trail into a new corner of the MCU", which differentiates it from Marvel Studios' previous two Disney+ series WandaVision and The Falcon and the Winter Soldier (both 2021) that are set shortly after Endgame.