Pre-Series
Blue Diamond was the second Gem to be created, only beaten by White Diamond herself. She was created along with Yellow Diamond, and Pink Diamond as a ruler of Homeworld. She was placed as the leading diplomat, and in charge of the diplomacy and aristocratic figures of Gem kind. Her reign continued throughout the millennium, making the Diamond Royal Court, and gaining other planets as time went by. During her reign, some of the earlier Gems came to her, and asked for her help in relocating Terra, sending out a search party to the abandoned Gem colony, much to their delight.
Blue Diamond was one of the three that confronted Kyra, and was seemingly defeated by him during their duel. One day after this, Lapis Lazuli informed her of the situation down on Earth, and that Pink Diamond had gone missing. Upon hearing this, Blue Diamond sent down herself and her court to investigate, only to be attacked by Rose Quartz and Pearl. This act was what triggered the coming Gem War. Blue Diamond seemingly drove Sapphire away with Ruby, and lost Lapis Lazuli as well, making her feel guilty over losing both members of her court. Despite this, she left their places in her court over the course of the Gem War.
Sometime after said Gem War, an unknown assailant came forward to her and became a threat on such a level that, according to her words "when he arrives, [she]'ll have to go.". She made a video message just prior to the apparent encounter, and it's unclear what exactly happened.
Season 2
The Crystal Gems managed to get contact with her on their way to her, and Blue Diamond found Sapphire and Lapis alive and well. She asked them who, or what else was with them, relieved that Kyra was seemingly not with them.
Upon their arrival, Blue Diamond happily welcomed the Crystal Gems and Mane Six to Homeworld properly, and got her own court members reacquainted with her as she had the others on tour to see the rest of Homeworld during their stay. As she allowed them to stay in her city, Blue Diamond aided them when she could. She properly identified Steven Universe as Rose Quartz, but didn't put any blame on him as it was someone else, though advised him to be careful. She offered a hand in their troubles, including talking to Yellow Diamond about Melanite, and sending out a few helpers when her court members went to the Abandoned Gem Settlement. When the Osicone first appeared, she at first denied it and believed it was just some tale and for the others not to worry, until Garnet went on and used her future vision on her. This triggered her to call on her forces to try and fight the Osicone, Blue Diamond herself staying back. When it was all done, she hosted a celebration for their victory, calling them heroes of Homeworld.
After the celebration, she met Kyra, and apologizes for not believing in him, though advised him to stay off Homeworld for the sake of Yellow Diamond.
Season 3
Throughout the season, Blue Diamond spent it helping Discord and Celestia set up a gift for the group in the form of a Warp Pad. During this she took the time to visit the Grand Galloping Gala, going there with help from Discord himself.
Season 4
She doesn't appear until the season finale: when White Diamond arrived to Homeworld, she and Yellow showed her around and were brought onto the White Diamond Space Station. When finding out about Sapphire's capture, Blue Diamond was told to shatter her, to which she refuses, saying she's one of her court members. She was then told to shatter Blue Pearl, and in defiance refused again saying she actually loved her pearl, as unorthodox as it was, before White Diamond poofed her. She came back later on, reformed and less willing to defy White Diamond. When the Crystal Gems and Mane six were brought in for execution, Blue Diamond was the first to react and took away White Diamond's weapon, pleading with her not to kill them. During this, she found out about Pink Diamond's "true" fate, but kept herself out of the following fight, distraught and conflicted about the situation altogether.
Season 5
After her return, she still remained completely distraught about the situation, thrown into a depression over the death of her sweet Pink diamond. This got White Diamond's attention sometime later, and after an unsuccessful attempt to bring her back around, White forbade her from going to Earth. Despite this, she and Blue Pearl went to earth anyway, which she believed was one last time, to see Pink Diamond's palanquin. She came across the others on Earth, and told them about the impending doom of The Cluster before she left for homeworld again. This didn't last too long however, as she was then captured by Grootslang, believed to be dead.
Season 6
After being rescued, she invited her saviors back to her city, and game them a gem object as a gift. However, Pearlis then arrived and informed her about their banishment from Homeworld, something she was unaware of up to that point. She kept Pearlis busy and instructed Blue Pearl to get the others to leave, biding them just enough time for their escape. Still trying to recover from the loss afterwards, she ended up discovering The Lost One growing in her part of homeworld, and after discovering a possible connection between it and Pink Diamond, she decided to leave it alone, though she did had it moved out of her city to a safer distance. After that, and seeing the gift it left for them, Blue diamond declared that whoever murdered Pink will pay dearly for their crime.
When the Humans arrived on Homeworld, she at first didn't pay them much mind, too distraught as a number of her Gems were starting to go missing, until Jamie told them of the team's secondary capture. She decided to fully defy her, and helped them on their way to the White Diamond Space Station in the Sun Incinerator. She got a message from her Diamond Communicator sometime later, told of Chamber 77. This got her and Yellow Diamond to investigate the science lab of the station, finally seeing Pink Diamond used as an experiment. She quickly confronted White Diamond shortly after that, but ended up captured herself as she and Yellow were next to be hybridized to form Green Diamond. Thanks to Onion and Starlight Glimmer, she went with Yellow Diamond to rescue Pink.
Season 8
During the first arc she was one of the Gems who went with White Diamond as part of her insisted vacation across the cosmos. She never truly agreed to the trip, but was more willing to go along with Steven's idea of teaching White, unlike Yellow. However, when they crash onto Orthix, she is hypnotized by White Diamond for a brief time before White realized she was flawed deeply and releases her. Even after that, Blue ultimately forgave her, referring her as "North Star".
Her role in the season is mostly minor, being put away from Homeworld thanks to Grogar.
My Little Universe II
Near the end of the season, she appears with Yellow Diamond as she was called to the Spirit council by Teal Garnet, in defense for White Diamond and Discord. She also joins them in the final battle with Grogar's Army, staying behind in the Realm of Corners to give the Harmony Gems time to stop his fleets from leaving Homeworld. However, during the fight she and Yellow got shattered by Grogar. She wasn't revived until after Grogar lost his powers, and Steven reviving them with his healing powers.