As an independently owned studio, Respawn Entertainment had previously developed Titanfall (2014) and its sequel Titanfall 2 (2016), both of which were published by Electronic Arts (EA) who eventually acquired Respawn Entertainment in 2017.
According to design director Mackey McCandlish, initial design on Apex Legends started before Titanfall 2 had shipped in 2016 and as of 2018 the entire Titanfall team at Respawn Entertainment was working on the project however, executive producer Drew McCoy stated that work on the game didn't begin until the spring of 2017. He also confirmed that the game had approximately 115 developers working on it, making it the studio's most labor-intensive project. Titanfall 2, by way of comparison, had around 85 developers.
While the initial development had been for a potential sequel to Titanfall 2, the success of PlayerUnknown's Battlegrounds as well as Respawn Entertainment's recent acquisition by EA had caused them to reconsider their plans. The studio had previously tested Titanfall concepts in a survival game format which they found to be promising, and subsequently started applying these design elements in a battle-royale framework. The designers decided that having the pilotable Titans (large mecha) from their previous games would not work well in a battle-royale setting and instead focused on creating strong character classes which felt appropriate for the Titanfall franchise.
Respawn Entertainment CEO Vince Zampella told Venture Beat that Apex Legends, as a live-service and free-to-play battle-royale game, was a new challenge for the studio and represented a new way for them of developing games. Their design philosophy was focused on "chasing the fun" and designing all the mechanics around team-based play, rather than solo play. The final decision on major design factors, such as the size of the teams, the number of teams and the size of the map, were all based on what felt "most fun" to the developers and were strongly guided by "gut feeling".
Design director Mackey McCandlish also stated that, with Apex Legends, they were looking to challenge the conventions of the still relatively young battle-royale genre and to add their studio's unique touch to that class of games. They felt that the choice of three-man squads and a limit of 20 teams gave players on average a greater chance to win and also felt more in line with the type of intimate gameplay they were hoping to achieve. McCandlish also claimed that the studio felt the need to create a "defensible space" in the battle-royale mode which could not be easily imitated, and that the communication system, the three-man squads and the smaller playing area were all aligned with this goal.
As part of the development process, the game underwent extensive playtesting to ensure that all elements felt fun and balanced. Collectively the developers spent 100 to 200 hours a day trying out the game, a process which executive producer Drew McCoy called "probably the most important part of development". In order to refine the game's non-verbal communication system, the studio playtested the game for a month without the use of voice chat and applied fake names to the playtesters to predict how most players would experience the game.
Uncharacteristically for EA, the development of Apex Legends was kept secret until its release with no prior marketing or advertising. The release of the game therefore came as a surprise when it was revealed in 2019, not least as until that point it had been assumed that Respawn Entertainment was working on a sequel to Titanfall 2 rather than a battle-royale game – in late 2017, a source at Respawn Entertainment had told Kotaku that Titanfall 3 was planned to be released towards the end of 2018. McCoy told Eurogamer that the surprise announcement was intentional as they were concerned of community backlash when it was revealed that, rather than working on a sequel to Titanfall 2, they had developed a free-to-play battle-royale game. McCoy believed that Apex Legends would be well received only if consumers were able to play as soon as it was announced, rather than spend a prolonged period of time hearing or reading about the game.