Before becoming involved with Stargate Command and, subsequently, the Atlantis Expedition, Weir was a skilled civilian diplomat who had travelled throughout the world. Daniel Jackson referenced her work in the first treaty for the Earth-Tok'ra Alliance.
She came to Stargate Command when President Henry Hayes expressed the desire to change the command into a civilian-run operation. Vice President Robert Kinsey also attempted to manipulate Weir as a pawn for his agenda, but she refused to go along. During her time there, she made a good impression on the staff there, and seems to have struck a very quick friendship with Dr. Jackson. (SG1: "Lost City, Part 1", "Lost City, Part 2")
When the System Lords arrived seeking help in killing Ba'al, Weir and Jackson negotiated with them. In a bold move to keep them talking, Weir asked that in return for killing Baal, they get his territory. She also granted political asylum to Camulus, whose domain had already been destroyed.
She stayed in the position as commander of the SGC for only a short time, being replaced by the newly-promoted Brig. General Jack O'Neill. She travelled to Antarctica to the Ancient outpost and eventually was named head of the Atlantis Expedition.
She gathered a large, international group of scientists for the expedition, including Rodney McKay. Weir also intervened in the military contingent that would be accompanying them, insisting that then-Major John Sheppard be included because of his carrying the Ancient Technology Activation Gene, despite the black marks on his record. (SGA: "Rising")
When Weir departed for Atlantis, she left behind her fiancé, Simon Wallis. She was forced to end the relationship for good when she found that she was stranded indefinitely in the Pegasus Galaxy. She later discovered that he had indeed "moved on" when she returned to Earth several months later. (SGA: "Letters from Pegasus", "The Intruder")
Commanders of Stargate Command