|Portrayed by Christine Baranski|
|Significant Others:||Kurt McVeigh|
She is initially skeptical when Alicia Florrick joined Stern, Lockhart & Gardner, seeing her as "entitled" and a junior associate who doesn't think she is one. She also offers to mentor Alicia Florrick, and while Alicia does not officially accept, Diane appears to be someone she can rely on. Every so often, Alicia would go to Diane for help, and she would be more than happy to oblige. During the competition between Alicia and Cary Agos, Diane initially seemed to favor Cary over Alicia, while Will favored Alicia.
Eventually, though, both partners saw the worth of both Alicia and Cary and had a hard time choosing on over the other. They end up keeping Alicia after she came through by getting Eli Gold as a client for the firm.
During this season, Stern, Lockhart & Gardner went through many challenges. There was a time when the firm was having financial troubles, and they had to layoff several of their employees.
The situation is aggravated when Will challenges the power of their fellow founding partner, Jonas Stern, whose presence at the firm was becoming sparse. When Stern returned when he needed a representation at court for a case against him, he chooses Alicia, who previously represented his daughter. When Diane and Stern find out that Will has been trying to push out Stern, they assume that it is because Stern had almost always agreed with Diane on their voting matters. Stern then goes on and disses both of the founding partners, particularly by telling Diane that he only hired her because it looked good to "have a woman in the office". Stern then decided to beat them to it and quit the firm to start his own law firm, taking their clients and a third of their business.
Diane was offered by the democratic ward and committee chairs to run for a position as a judge in the upcoming election, and that she was a shoo-in because she is a woman and will be campaigned for by democrats. Diane considered it, but running would mean she must divest herself from the firm. Although Diane wanted it, the committee later returned to her to tell her that she could not run yet because of her client roster, although it is most likely because the latest case she helped with involved revealing the corruption of another judge that the committee favored, and that if she did run, she would have to compete with them.
During season 4 Diane is offered an Illinois Supreme Court Justiceship.
He hired Diane as senior partner because he thought that it would look good if there was a female senior partner. However later in that episode, when they face each other Diane say "You hired me because I was the best lawyer in your firm." and Stern nods. He seemed to prefer her to the other partner Will Gardner because he voted with her 90 percent of the time. He also, used to mentor Diane in her earlier years as stated in season 1. When he returned after an extended period of absence, Diane was worried that it would give their department bad publicity because he was being accused of DUI and battery. Diane was the first person he told that he was leaving Stern, Lockhart & Gardner to start his own law firm and he was going to take their clients and a third of their staff.
Not much is shown about Diane and Kurt's relationship, but they have occasional dates. In season 3 it is revealed they haven't seen each other for a year. In season 4, they reconnect and kiss on either Diane or Kurt's couch. Diane reveals that they are engaged and they get married in season 5.
Will and Diane are name partners at their lawfirm Lockhart/Gardner. They are very good friends.
- She has a pet dog named Justice.
- She is a democrat.
- She is anti-gun