The Psi Corps and President Clark, whose government has discovered Shadow vessels buried in Earth's solar system, begin to harness the vessels' advanced technology. The Clark administration continues to become increasingly xenophobic and totalitarian, and uses a military incident as an excuse to declare martial law. This triggers a war of independence on Mars, which had long had a strained political relationship with Earth. Babylon 5 also declares independence from Earth, along with several other outlying Earth Alliance colonies. In response, the Earth Alliance attempts to retake Babylon 5 by force, but with the aid of the Minbari, who have allied with the station against the growing Shadow threat, the attack is repelled.
Becoming concerned over the Shadows' growing influence amongst his people, Centauri ambassador Londo Mollari attempts to sever ties with them. Mr. Morden, the Shadows' human representative, tricks him into restoring the partnership by engineering the murder of Mollari's mistress while putting the blame on a rival Centauri House. Open warfare breaks out between the Shadows and the alliance led by Babylon 5 and the Minbari. It is learned that genetic manipulation by the Vorlons is the source of human telepathy, as it is later discovered that Shadow ships are vulnerable to telepathic attacks. Displeased at the Vorlons' lack of direct action against the Shadows, Captain John Sheridan browbeats Vorlon ambassador Kosh Naranek into launching an attack against their mutual enemy. Kosh's deeds lead to his subsequent assassination by the Shadows.
Former station commander Jeffrey Sinclair returns to Babylon 5 to enlist the aid of Captain Sheridan, Delenn, Ivanova and Marcus in stealing the Babylon 4 space station and sending it 1,000 years back in time to use it as a base of operations against the Shadows in the previous Minbari-Shadow war. Undergoing the same transformation as Delenn at the end of Season 1, Sinclair transforms into a Minbari and is subsequently revealed to be the actual Valen of Minbari legend, rather than a reincarnation. Spurred by the reappearance of his assumed-dead wife (who now works for the Shadows), Sheridan travels to Z'ha'dum, the Shadow homeworld, in an attempt by them to recruit him. However he instead destroys their largest city in a kamikaze nuclear attack, and is last seen jumping into a miles-deep pit to escape the explosion. Garibaldi, during a fight with Shadow vessels, goes missing.
丹·史蒂文斯 朱迪斯·赖特 希·庞德 阿西夫·曼德维 迈克尔·阿伦诺夫 b 菲利普·埃廷格 胡安尼·费利兹 Hampton Fluker 约翰·本杰明·海基 马琳·爱尔兰 Hayward Leach 斯蒂芬·鲁特 才那扎·乌奇
马修·瑞斯 凯特·奥弗林 斯蒂芬·鲁特 金斯顿·鲁米·索斯威克 凯文·卡罗尔 戴尔·迪奇 Ava Gaudet 威廉·希尔 戴维·阿姆斯特朗 伊莱·D·戈斯 Jimmy Shirts 伊恩·莱昂斯 克里斯托弗·C·詹姆斯 Shawn Jain Kevin F. Conway Pat Fitz 雷纳尔多·特罗亚 Lee DiFilippo Vincent Flynn Suzanne Gillies
安德鲁·浩二 阿奇·马德基 安德鲁·霍华德 哈里·米歇尔 苏菲·特纳 雅各布·福琼·劳埃德 塔拉·萨莫斯 多米尼克·马夫海姆 斯派克·莱顿 莎拉·贝尔彻 Yusra·Warsama 戴安娜·贝穆德斯 艾莉·詹姆斯 肖恩·梅森 朱丽安娜·库洛卡娃 埃洛伊丝·托玛斯
本尼迪克特·加勒特 叶夫根尼娅·冬妮娜 Liraz Chamami Edward Sonnenblick Amir Haddad 尤西·马什克 弗拉基米尔·弗里德曼 Ronn Talia Lynne
塔哈·拉希姆 伊祖卡·霍伊尔 Jessica Barker-Wren 丹尼尔·贝茨 芬恩·本尼特 乔丹·朗 斯蒂文·埃尔德 Adil Akram 埃迪·马森 凯瑟琳·麦克马克 劳里·戴维森 肯·恩沃苏 莉奥妮·贝尼希 山姆·特劳顿 布莱恩·F·奥博恩 优素福·凯尔科尔 安东·瓦朗西
奥德雷·弗勒罗 梅迪·内博 布鲁诺·桑切斯 玛丽·德纳尔诺 贝兰奇尔·麦克尼斯 塞普里安·加尔丹 诺埃·范德沃尔德 塞德里克·舍瓦姆 Christopher Bayemi 吕菲斯 杰里米·勒温 克洛蒂尔德·埃斯姆 多多·马斯塔 帕特里克·薛内斯 尼古拉斯·马丁内斯 米歇尔·莫雷蒂 玛拉·泰利安 Akache Busiah Cédric Le Maoût