This afternoon’s episode (repeat, of course) of Law & Order had S. Epatha Merkeson as the mother of the two victims. Later in the series, she signed on as Lieutenant Van Buren. So that got me to wondering who else has played multiple parts on the series?
The guy who plays detective Lenny Brisco played a Defense Attorney in an episode aired during one of the first few seasons.
belladonna: Wasn’t he playing Lenny Brisco, cop who became defense attorney for a time, though?
Most notably, Jerry Orbach appeared as a defense attorney (in the Betty Broderick knockoff episode with Shirley Knight as the defendant who kills her ex-husband and his new wife) before he took on his role as Lenny Briscoe.
But a fan who goes by the name of MindHarp, an L&O junkie extraordinaire, maintains the definitive list of actors who have appeared on Law & Order more than once, known as “Repeat Offenders.”
Law & Order “Repeat Offenders”
Note that this list only covers those who have appeared as different characters, like Anthony Heald, who has been a slimy attorney with political aspirations and an IRA hitman or Aida Turturro who has been a homegirl and the funkiest receptionist in history.
Actors who have appeared as recurring (but not regular) characters (Tovah Feldshuh’s Danielle Melnick or Donna “Ex-Mrs. Guiliani” Hanover’s Judge Bourke) are not listed as repeat offenders, but many can be found (along with all of the regular cast members past and present) in the Law & Order Kevin Bacon Game Results page, along with their Kevin Bacon degrees number. 
Courtney B. Vance, ADA Ron Carver on “Law & Order: Criminal Intent” was a defendent in a 1995 episode of L&O an a ‘mayor’s aid’ in a 1990 episode.
Jerry Orbach played a part in 1991 before he became a regular member of the cast, as mentioned above.
Man, I would never have even dreamed I would be answering a post like this, but my girlfriend got hooked on this show this summer and spent 2-3 hours a day watching it.
I don’t think so. I can’t remember exactly but I first saw the defense attorney episode in reruns after getting used to him as a cop and I believe I would have noticed if he had the same name…
Well, on preview, TeaElle beat me to it. Ah well, I’m posting anyway dammit. 
To clarify entirely:
Jerry Orbach guest starred as defense attorney Frank Lehrman in Episode 2:02 (second ep of season 2) entitled “The Wages of Love.” The original air date for the episode was September 24, 1991. As I mentioned, he represented Melanie Cullen (played by Shirley Knight) who was accused of killing her ex-husband and his new wife in a dramatization of the real-life case of Betty Broderick.
Orbach joined the regular cast as Detective Leonard “Lenny” Briscoe midway through the third season in “Point of View” (Episode 3:09), The original air date for that episode was November 25, 1992. In that episode, veteran Broadway actress Elaine Stritch was attorney Lanie Stieglitz, and she defended Mary Kostrinski (repeat offender Lisa Eichorn), a woman accused of murder who claimed that she killed in self-defense against a rapist.
In addition, there has been massive cross-pollination between the various L&O shows and Oz, including:
J.K. Simmons (Oz:Shillinger, L&O: Dr. Emil Skoda)
B.D. Wong (Oz: Father Mukada, L&O SVU: Dr. Huang)
Dean Winters (Oz: Ryan O’Reily, L&O SVU: Detective Cassidy)
Christopher Meloni (Oz: Keller, L&O SVU: Detective Stabler)
Kathryn Erbe (Oz: Bellinger, L&O CI: Detective Eames)
This only counts major recurring characters. Numerous actors have worked on one show while doing guest shots on the others.
Further, numerous actors from The Practice have done guest shots on L&O. Camryn Manheim is the only one who played a lawyer, but all the others (Steve Harris, Michael Badalucco, Lisa Gay Hamilton, Kelli Williams, as well as Manheim in a different appearance) played criminals or suspected criminals.
Great info, folks! Now, does anyone know why “Maureen Girard” was picked as the name of one victim in one episode? I ask because I actually had an English teacher with that name at my community college.
Bryan Ekers, The cross-pollination of actors between L&O and Oz is also in effect between L&O and Homicide: Life on the Streets. The three universes have many, many intersecting lines, not he least of which being Detective John Munch, played by Richard Belzer, who began on Homicide and is now a member of the squad on L&O SVU.
Camryn Manheim is the only cast member of The Practice who played an attorney on L&O, but she’s never been a criminal nor a suspect. In the episode “Life Choice” she was interviewed as a spokesperson for a pro-life group, in “Benevolence,” she was a defense attorney and in “Nurture” she was the far too lax foster mother of a little girl who was kidnapped. In that episode, her boyfriend was a suspect, but she never really was.
Monty, the names on Law & Order are reputedly chosen by randomly selecting names from lists of common names which are appropriate to the character’s age, gender and ethnicity. Chances are that Maureen Girard was simply the combination that was plucked from the list.
The one known exception to this would be William Dell, the evil special prosecutor in the last L&O/Homicide crossover. His name was specifically chosen as a jab at Dell Computers, due to a dispute that Dick Wolf (executive producer) was having with the company when the episodes were produced.
I dunno. At the very least, I seem to recall the detectives accusing her of child neglect or endangerment in the episode. She certainly was crossing the line when she let her boyfriend stay over, despite a court order keeping him away from the foster child in that episode.
So for the sake of a general rule (all the Practice actors that have appeared on L&O have played criminals or suspected criminals), I’m willing to be generous.
Six Feet Under’s Lauren Ambrose (the redheaded daughter) has been on Law&Order three times, though I only remember her as a band student and the mentally handicapped rape victim (she did an amazing job, not too cutesy).
Homicide and L&O must take place in the same universe, because they did two crossovers.
When Briscoe and Munch first met, in an episode of Homicide, they learned (to Munch’s horror) that they have an ex-wife in common.