After seven long seasons, Marvel’s Agents of S.H.I.E.L.D. can no longer claim to be aligned with the Marvel Cinematic Universe’s timeline - not after skipping Thanos’s Snap and the five-year Blip that followed. But along the way, Agents of S.H.I.E.L.D. managed to cross over with the MCU far more than it’s given credit for - with some of those moments going well beyond references and Easter eggs to truly expand upon the franchise.
Despite debates over canon and continuity, there’s no doubt that the events of Agents of S.H.I.E.L.D. belong firmly within the history of the Marvel Cinematic Universe as a whole. Not every S.H.I.E.L.D. storyline has had something to do with The Avengers or Guardians of the Galaxy, but plenty have - including some of the show’s best.
Though it is often described as being divorced almost entirely from the Marvel Cinematic Universe, in a way, Agents of S.H.I.E.L.D. has been perpetually crossing over with the MCU for all seven seasons in the form of Phil Coulson, who continues to be one of the series’ main characters - in a way.
The show shocked fans of the franchise right out of the gate by bringing Coulson - the MCU’s first major casualty in 2012’s The Avengers - back to life for the pilot, spending much of the first two seasons unraveling the mystery of how that came to be. Since that first alien-blood-infused resurrection, Coulson has perished and been brought back again on multiple occasions through methods as diverse as life-model decoys and demons from the Fear Dimension. Or, as he puts it, “Dying is my superpower.”
The Kree civilization has made a colossal impact on the Marvel Cinematic Universe, from Ronan the Accuser’s turn as villain in Guardians of the Galaxy to being Carol Danvers’s alien abductors in Captain Marvel, but their first official MCU appearance came in Agents of S.H.I.E.L.D. (AoS) - and it was a rather important one.
Kree blood, drained from the partial cadaver of a Kree warrior possessed by SHIELD for some unknown reason, proves to be the magic behind Project TAHITI, the top-secret initiative that brings Coulson back to life. Eventually, Captain Marvel would shine some light on how exactly that body ended up in SHIELD custody, making the whole storyline a retroactive crossover.
But by then, living and breathing Kree had already made several antagonistic appearances on AoS.
As the highest-ranking member of the titular organization, it just wouldn’t have felt right to not have Nick Fury involved in Agents of S.H.I.E.L.D. in some capacity - and so he makes not one, but two cameos in the series’ first season. Since then, his impact has continued to be felt, even without any further on-screen appearances by Samuel L. Jackson.
Fury shows up at the end of the series’ second episode to scold Coulson for wrecking a plane. After having his name evoked constantly for the rest of the first season, he appears again in the finale, helping Agents Jemma Simmons and Leo Fitz out of a deadly situation - and appointing Coulson as the new Director of SHIELD.
He also hands over the Toolbox, a vibranium-protected cache of all of SHIELD’s files and data, which has continued to be integral to the show’s plot.
The first - and only - major character unaffiliated with SHIELD to cross over from the MCU to Agents of S.H.I.E.L.D. is Lady Sif, who was featured in both of the series’ first two seasons. She joins Coulson and the others in Season 1 to bring an Asgardian fugitive - Lorelei, sister of the Enchantress - to justice in the wake of Thor: The Dark World.
Sif appears again in Season 2, but in a significantly less-friendly fashion. As it would turn out, she had been mindwiped by the Kree and sent on a mission to take out all Inhumans, including SHIELD’s own Quake, but the whole thing gets sorted out in the end, and Sif parts with the agents on good terms - only to never again appear in the Marvel Cinematic Universe.