Citadel promises to bring fan-favourite characters along for "one final, sentimental journey" in Commander Shepard's trilogy, including Miranda, Garrus, and Wrex.
The file size of the content is so big that Xbox 360 owners will be required to download it in two chunks, having to pay 1,200MSP for the first part and then getting the second for free. Citadel will not function on the Xbox 360 without the first pack.
PC and PS3 users will get all of Citadel in one download. The pack will be released on March 5 for $14.99/1,200MSP.
"When a sinister conspiracy targets Commander Shepard," wrote BioWare community manager Chris Priestly on BioWare's forums, "you and your team must uncover the truth, through battles and intrigue that range from the glamour of the Citadelís Wards to the top-secret Council Archives. Uncover the truth and fight alongside your squad--as well as the cast from the original Mass Effect and Mass Effect 2."
In addition to Garrus, Miranda, and Wrex, BioWare has teased a return for Liara, James, and Kaidan in the pack's screenshots.
After players have finished the main chunk of content, Citadel will contain an additional hub to explore, promising both minigames and additional story content.
"When the adventure is over, reconnect with your favorite characters from the Mass Effect Trilogy, try your luck at the Citadel's Silver Coast Casino, blow off steam in the Armax Combat Arena, or explore and furnish Shepard's own living quarters on the Citadel. With unique content and cinematics featuring your friends and romance interests in the Mass Effect trilogy, Mass Effect 3: Citadel offers one final chance to see the characters you have known for years and rekindle romances."
"The team has poured heart and soul into Mass Effect 3: Reckoning and Mass Effect 3: Citadel. As the launch of these chapters near, the feeling around the studio is bittersweet," said executive producer Casey Hudson.
Alongside Citadel, BioWare formally announced the previously rumoured Reckoning multiplayer pack, which will be released for free on February 26.
"Newfound allies join the multiplayer war for survival in Mass Effect 3: Reckoning," said Priestly. "The Geth Juggernaut, Female Turian Raptor, Talon Mercenary, Alliance Infiltration Unit, and more take up arms to stop the Reaper threat. Smash your enemies with the Biotic Hammer as you lay waste to the battlefield as the Krogan Warlord."
"Wield 7 new weapons for multiplayer, including the Geth Spitfire Assault Rifle, Venom Shotgun, Lancer Assault Rifle, and amplify your arsenal with new equipment and weapon mods featuring the Geth Scanner and Assault Rifle Ultralight materials."
For more Mass Effect 3 information, check out GameSpot's previous coverage.