•
Dylan McDermott as Bobby Donnell (seasons 1–7; guest season 8), the senior partner of the firm who struggles with his conscience and the idea of being a lawyer. •
LisaGay Hamilton as Rebecca Washington (seasons 1–7), the firm's first receptionist and paralegal. She later passed the bar exam and became an associate. •
Steve Harris as
Eugene Young, the second highest-ranking partner at the firm and later senior partner who is more strongly devoted to the letter of the law and legal ethics than his colleagues. Later he even becomes a judge. •
Camryn Manheim as Ellenor Frutt, an associate and later senior partner at the firm who brought in various nefarious clients. A recurring gag on the show was that the men she dated often turned out to be murderers. •
Kelli Williams as Lindsay Dole (seasons 1–7), an associate at the firm and, later, wife of Bobby Donnell. •
Michael Badalucco as Jimmy Berluti, an associate and later partner at the firm from a working-class background. Jimmy often struggles with his conscience, loneliness, feelings of inadequacy, and a gambling addiction. •
Lara Flynn Boyle as Helen Gamble (seasons 2–7), an Assistant District Attorney and friend of the firm partners who was relentless in her attempts to prosecute those who do wrong. •
Marla Sokoloff as Lucy Hatcher (seasons 3–7; recurring season 8), the firm's wise-cracking, nosy receptionist who was hired after Rebecca became an attorney. She later became a part-time counselor for rape victims in addition to her job as a receptionist. •
Jason Kravits as Richard Bay (season 5; recurring season 4), a diminutive, hard-nosed Assistant District Attorney who believed in the guilt of all those he prosecuted. •
Ron Livingston as Alan Lowe (season 6), an Assistant District Attorney who replaced Richard Bay. •
Jessica Capshaw as Jamie Stringer (seasons 7–8), a high-strung, promiscuous Harvard Law School graduate and associate at the firm. •
Chyler Leigh as Claire Wyatt (season 7), Lindsay's associate at her new practice. •
Rhona Mitra as Tara Wilson (season 8), a paralegal and law student. She would later appear in
Boston Legal as an attorney. •
James Spader as Alan Shore (season 8), an amoral associate and an old friend of Ellenor. He would later appear in
Boston Legal. == Recurring cast ==