Warning: Spoilers from Avengers: Endgame are ahead.
With she's now a major part of the Marvel Cinematic Universe, Captain Marvel's screen time in Avengers: Endgame is both amazing and... also a little disappointing. While Carol Danvers (Brie Larson) is prominently featured in every single poster for the movie and gets a fair share amount of screen time in every released trailer, her involvement in the greater story is minimal. Yes, she has some major things to do to set the story in motion, but if you think Captain Marvel just hangs out at Avengers headquarters eating bread with Thor (Chris Hemsworth), think again. She’s the most powerful Avenger, and also the newest Avenger, so where was Captain Marvel during Avengers: Endgame?
Captain Marvel shows up at the very beginning of the movie to do a very important thing: Save Tony Stark (Robert Downey, Jr.) from space (while it’s never outright explained, we’re led to believe that the end credits scene from Captain Marvel is what brings her to HQ in the first place as her first introduction to everyone, and from there she heads into space before the events of Endgame even begin). Because she is strong and mighty she literally flies the broken spaceship down to Earth with her bare hands, and then travels with everyone else to defeat Thanos (Josh Brolin) on his garden planet. They do, but things are still pretty bad, and the group goes their separate ways — including Captain Marvel. We later see Carol Danvers (with a new haircut), via hologram, talking to Black Widow (Scarlett Johansson) about her continuing work with the Avengers, but then she heads back into space.
She eventually shows back up during what is literally the third act of the third act of the movie, and does her signature “I’m going to fly through this spaceship and destroy it!” move before joining the rest of the heroes in their fight. But, something like two hours has passed between her appearances. It’s not a stretch to wonder where was she the entire time. Here are a few likely reasons she was otherwise engaged:
She was with the Skrulls
At the end of Captain Marvel, our hero heads off to help the Skrulls find a new home planet after the Kree destroyed theirs. Hopefully, over the last 30-ish years, she’s managed to help them, but it’s totally possible that she’s still working alongside them (and protecting them) from danger. Earth has a handful of Avengers, but the Skrulls likely only have Carol.
There were a lot of other planets that needed help after Thanos destroyed them
Carol makes this comment towards the beginning of the movie when she’s questioned as to where she’s been. Thanos doesn’t just destroy half of the population on Earth, but takes his Infinity Stones elsewhere in the galaxy, too. Seeing as how she’s already well-traveled through space, it’s Carol’s job to help the other planets affected by the Mad Titan.
No one thought to ask her for help
Never once did any Avenger go, “Hey, maybe we should call Carol again on that pager.” That would have made things like time travel probably 200% easier.
Avengers: Endgame would have been 90 mins if Captain Marvel were left in charge of the plan
The joke all along was that Captain Marvel would be the one to defeat Thanos. If she had shown up during Infinity War things would definitely be different, because during Endgame she’s actually able to get the Infinity Gauntlet off his hand. That is mad impressive. The Avengers needed to struggle for a bit before calling in major reinforcements.
Showing too much of Captain Marvel would have been a spoiler for her other movies
It’s possible that there were more Captain Marvel scenes filmed that somehow didn’t make the three hour cut of the film. Maybe it was a conscious decision not to include them, considering we’re all just getting to know Captain Marvel ourselves. Let her have the spotlight in her own movies, not during Tony Stark’s grand swan song. Also, it’s been almost 30 years in the Avengers timeline since Captain Marvel, and maybe there was just too much new Captain Marvel stuff to cover. Easier to cut it.