At the Television Critics Association winter press tour in January 2018, The CW president Mark Pedowitz said he was "optimistic" and "confident" about Arrow and the other Arrowverse shows returning next season, but added that it was too soon to announce anything just yet. On April 2, The CW renewed the series for its fourth season. Marc Guggenheim stepped down as co-showrunner at the end of the third season, with co-showrunner Phil Klemmer originally set to emerge as sole showrunner for the fourth season. However, Keto Shimizu ultimately replaced Guggenheim as co-showrunner, to serve alongside Klemmer for this season. Guggenheim, the series' co-developer along with Klemmer, remained involved as an executive consultant.
Writing
Phil Klemmer said that Mallus, the Big Bad of the third season, was "a sort of bellwether of bad guys to come in Season 4", which he said would go deep into the "world of fantastic myths and monsters", without abandoning the time travel nature of the series. He also said the season would further explore the Time Bureau, which was introduced in season three. Klemmer added that at least one of the Legends would "" in the season. Tala Ashe, who joined the series as Zari Tomaz during the third season, said the fourth season would further explore the character's backstory, in addition to the prejudice and xenophobia experienced by her. Courtney Ford, who recurred in the third season as Damien Darhk's daughter Nora, hoped the fourth season would explore what the character is without the influence of her father and Mallus. Klemmer compared Neron, the season's Big Bad, to technology entrepreneur Elon Musk, calling him a "disruptor" in Hell, similar to how Musk affected transportation with Tesla electric cars. Originally, the character of Hank Heywood was designed as the Big Bad of the season, however, when the writers saw Tom Wilson's performance and got to know him as a person, the character was rewritten as more sympathetic and likable. The original plan of turning Nate Heywood into a more sinister character because of his father was also abandoned in favor of a plotline where Hank is turned instead.
Casting
Main cast members Brandon Routh, Caity Lotz, Amy Louise Pemberton, Dominic Purcell, Nick Zano, and Tala Ashe return from previous seasons as Ray Palmer / Atom, Sara Lance / White Canary, Gideon, Mick Rory / Heat Wave, Nate Heywood / Steel, and Zari Tomaz, respectively. Maisie Richardson-Sellers, who played Amaya Jiwe / Vixen in seasons two and three, also returned as a series regular, portraying a new character named Charlie, one of the season's magical fugitives. While Sellers spoke with an American accent when playing Amaya, she speaks with her native British accent when playing Charlie. In July 2018, Ramona Young was added to the main cast as Alaska Yu, though her character was ultimately named Mona Wu. Matt Ryan, Jes Macallan and Courtney Ford, who recurred in the third season as John Constantine, Ava Sharpe and Nora Darhk respectively, were promoted to regular status for the fourth season. Keiynan Lonsdale, who portrayed Wally West / Kid Flash as a regular in the latter half of the third season, did not return in the same capacity for the fourth season. He cited his reason being his desire to seek other acting opportunities. This is the first season not to feature Arthur Darvill, who starred as Rip Hunter in the first two seasons, and recurred in the third season. It is also the first not to feature Victor Garber and Franz Drameh, who starred as Martin Stein and Jefferson Jackson respectively, in the previous seasons.
Filming
Production for the season began on July 5, 2018, in Vancouver, and concluded on January 25, 2019.
Music
On April 16, 2019, WaterTower Music released "I Surrender", a single from the episode "Séance and Sensibility" for free. The single was performed by actors Tala Ashe, Sachin Bhatt, Ramona Young, Brandon Routh, Courtney Ford, Caity Lotz, and Maisie Richardson-Sellers.
Marketing
The main cast of the season as well as Phil Klemmer attended San Diego Comic-Con on July 21, 2018, to promote the season. On October 15, 2018, Routh released a mock political ad on his Twitter page, voiced by Zano. The ad jokingly claimed that Arrow, The Flash, and Supergirl were trying to keep attention away from Legends of Tomorrow, followed by many headlines as well as real and fake quotes praising the series.
Release
Broadcast
On June 20, 2018, The CW released its fall schedule, revealing that the series would move from the 8:00 pm Monday time-slot to the 9:00 pm time-slot, to serve as the lead-out to Arrow. The season began airing in the United States on The CW on October 22, 2018.
Home media
The season was made available for streaming on Netflix in late May 2019.
