Kurt McVeigh is a ballistics expert and love interest of Diane Lockhart. Diane hires him during the first season to consult on a homicide case, despite Kurt's assurances that he would resign if he learns her client is guilty. The pairing of Diane with Kurt is a culture clash of sorts, pitting a lifelong liberal trial lawyer and gun-control advocate against a conservative outdoorsman and gun enthusiast Diane once called "the Marlboro Man."
Kurt is a member of the Tea Party and an avid Sarah Palin fan. During their first meeting, he chuckles at Diane's prized picture of herself with Hillary Clinton. He later sends her a copy of Palin's bestselling autobiography, Going Rogue, and upon her first visit to his ranch, he makes a point of putting out a picture of himself with the former Alaska governor. Their clashing politics at first makes Diane uncomfortable, but she soon finds herself unable to resist his charms. Additionally, their relationship causes problems with Diane's firm constantly hiring him, as sleeping with a client would be unethical.
Diane and Kurt marry in season five. She detests his friends, all attractive women ballistics experts. Kurt sees no one but Diane. Diane, in turn, makes a very easy decision to turn down advice from her oldest friends, who want her to dump him because of his conservative views.
In the series finale, "End," during Peter Florrick's corruption trial, Kurt is put in the awkward position of testifying for the prosecution against Peter, who is Diane's client. Alicia and Lucca try to discredit Kurt on the stand by forcing him to reveal an extramarital affair Kurt had with another ballistics expert. In the final scene, Alicia, attending her husband's resignation speech as governor, happens upon Diane in a back hallway, who slaps Alicia hard across the face.
Kurt and Diane's relationship continues in The Good Fight.