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 goes to Diane for help, and she is happy to oblige. During the competition between Alicia and Cary Agos, Diane initially seems to favor Cary over Alicia, while Will favors Alicia.
Eventually, though, Diane and Will each see the worth of Alicia and Cary and have a hard time choosing one over the other. They end up keeping Alicia after she secures Eli Gold as a client for the firm.
During this season, Stern, Lockhart & Gardner goes through many challenges. The firm experiences financial troubles and has to lay off a spate of employees.
The situation is aggravated when Will challenges the power of their fellow founding partner, Jonas Stern, whose presence at the firm is becoming sparse. When Stern needs 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 it is because Stern has almost always agreed with Diane on their voting matters. Stern lashes out at the founding partners and tells Diane that he only hired her because it looked good to "have a woman in the office". Stern then decides to quit the firm and start his own law firm, taking their clients and a third of their business.
Diane receives an offer by the Democratic ward and committee chairs to run for a position as a judge in the upcoming election. She is told she is a shoo-in because she is a woman and will be campaigned for by Democrats. Diane considers it but running would mean she would need to divest herself from the firm. Although Diane wants the spot, the committee later returns to her to tell her that she cannot run because of her client roster, although it is most likely because a recent SLG case revealed the corruption of another judge that the committee favored, and if she runs she will have to compete with them.
Throughout Season 2 Diane jockeys to maintain her position at Lockhart/Gardner & Bond. Derrick Bond, the new managing partner, works to oust Diane from the firm and even appears to gain Will's support for a time. After Diane and Will clear the air, they go to work to outvote Bond so they can oust him instead.
During this period of professional upheaval Diane represents Kurt McVeigh, her onetime romantic interest, in court. He expresses a desire to take a trip with her after the trial and begin a relationship -- or even a life -- together. Diane chooses to focus her energies on the fight at Lockhart/Gardner & Bond, telling Kurt that she made the decision to prioritize her career "a long time ago." In the next episode Will and Diane successfully outvote Bond and he leaves the firm.
During season 4 Diane is offered an Illinois Supreme Court Justiceship by Peter Florrick.
Season 5 Edit
After Will's death, Louis Canning joins the firm. Diane to join Florrick, Agos.
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