On July 3, 2016, Thomas Astruc explained that Season 3 was being written at the same time as Season 2, in order to avoid a hiatus between seasons.  As of January 14, 2017, the season was still in the writing process.
At a panel at New York Comic Con on October 7, the crew revealed a new sneak-peek image of the peacock superhero, with the image labelled as being for Season 3. They also showed concept art of Duusu, whose image noted her as appearing in both Season 2 and Season 3. In a teaser for a Los Angeles Comic-Con panel for October 30, Jeremy Zag revealed that a fan of the show would be akumatized in Season 3.
Astruc confirmed at Comic Con Paris on October 23 that the crew was currently writing Season 3, and because they set the bar very high for Season 2, the writers had a lot of pressure to improve from that with Season 3.
On March 1, 2017, Astruc announced on Twitter that the crew had written three episodes in one day, saying that "on the menu" are a "big party, apocalypse, and DBMAT." The next day, he added a picture of what DBMAT stood for: "Dragon Ball Martial Arts Tournament" from the franchise Dragon Ball. Later that month, on March 22, director Wilfried Pain revealed that the production of the season was in its storyboarding and animatic phases.
When asked on April 10, 2017 if the show will include new heroes that are more diverse, the official Miraculous Ladybug Tumblr blog replied that it would, noting, "Wait until you see Season 3!" In response to a user asking about his day, Astruc posted that the crew had finished writing another episode that "will blow [their] mind" and only had six more episodes left to be written for Season 3.
On Twitter on May 1, 2017, Astruc posted that he was working on finishing a story before the next day, noting that in it, Marinette and Adrien will be together, with Astruc calling it "EXTREME Adrienetting." On May 17, during a live event for the series, Princess Fragrance was confirmed to return for the season, along with other akumatized villains, in a huge event.
At Dokomi 2017 on June 4, Astruc and Pain revealed that in a week, the crew would be creating the Season 3 finale.
In a press release video from TFOU on August 31, 2017, new information surfaced about a two-part special previously teased in May, "Heroes' Day," with "the best of the worst akumatized villains" returning and fighting the superheroes. Ultimately, however, Heroes' Day was released in Season 2 instead. 
On December 28, 2017, in an interview, Pain noted that there is an episode in Season 3 that involves theater, and another episode will include a game that has references to anime.
On March 20, 2018, Pain shared a rough animation of a Season 3 episode under the production code LB317. On May 6, 2018, a third-season poster was shown at the CONQUE event in Mexico. During the Japan Expo 2018 panel on July 9, 2018, Sébastien Thibaudeau revealed that the 78th episode had moved the team to tears. He hoped this would have the same effect on the spectators. On July 17, 2018, Morade Rahni, a storyboard designer, posted on Twitter an animatic of Rena Rouge detransforming, tagging the image with #Season3.
On November 2, 2018, Adrien's European Spanish voice actor, Jesús Barreda, announced that two episodes of Season 3 were to be dubbed the following week. Astruc noted on November 4 that the release range of Season 3 in France depends on the time of year, commenting, "Usually, in France, they like to launch new stuff for Easter or September. And it depends if there's a sufficient amount of episode[s]. So one sure thing only: no release date you could read can be accurate." Similarly to Barreda, the English voice actor for Tikki, Mela Lee, announced on an Instagram story on November 7 that English dubbing of Season 3 episodes was also to start the following week.
On November 21, 2018, the third season was confirmed to be in the recording process in Portugal. Three days later, Disney Channel Spain announced that they would premiere "Chameleon" on December 1, 2018. Similarly, Disney Channel Portugal announced that they would also be premiering the season that same day.
On December 6, 2018, Jeremy Zag revealed big spoilers of new transformations in the third season.
On December 8, 2018, CCXP 2018 released a clip from "Weredad" during a script reading by Brazilian Portuguese voice actors Fabricio Vilaverde (Cat Noir) and Jéssica Vieira (Ladybug).
On December 10, 2018, it was announced that Season 3 would premiere on Disney Channel UK at the start of the new year. The premiere actually occurred on March 4, 2019.
On January 28, 2019, Family Channel Canada announced they would air the first 9 episodes of Season 3 during February. This was later cut back to 5 episodes, which is all they actually did air that month.
On February 1, 2019, RTS Deux revealed all of the episode titles and synopses for this season.
The third season had its official premiere in France on April 14, 2019.
The first half of Season 3 was officially released on Netflix on August 1, 2019.
On September 5, 2019, Selah Victor posted a picture of the Season 3 finale, regarded as, THE BEST EPISODE EVER"[]