Other characters
Laurie (Lisa Edelstein): Sam Seaborn's friend. Law student working as a call girl (season 1 and mentioned several times in 2).
Al Kiefer (John de Lancie): Democratic pollster who had a short relationship with Joey Lucas. The senior staff cannot stand him, and when Joey's abilities became apparent, she takes over his previous role as the Bartlet administration's top pollster (season 1).
Larry Claypool (John Diehl): Freedom Watch lawyer (Seasons 1, 4) who spends his time filing lawsuits against President Bartlet and his staff in hopes of bringing down the administration
Bernard Thatch (Paxton Whitehead): Head of the White House Visitor's Office (Ep 2.10, Ep 6.07).
Ann Stark (Felicity Huffman): Toby Ziegler's former friend, until she betrays him when he tries to broker a compromise on patients' rights. Chief of Staff to the Senate Majority Leader (Ep 2.11)
Roberto Mendoza (Edward James Olmos): Short-list nominee and later confirmed Associate Justice of the Supreme Court. (Ep 1.9, Ep 1.15)
Lisa Sherborne (Traylor Howard): Sam Seaborn's former fiancée who now works for Vanity Fair. Sam broke off their engagement because he wanted to leave the New York scene and work at the White House (Ep 3.11).
Dr. Stanley Keyworth (Adam Arkin): A psychiatrist from San Francisco who specializes in trauma cases. He is asked by Leo McGarry to see Josh after Josh yells at the President. Staff Therapist for the American Trauma Victims Association (ATVA), has several sessions as the President's therapist as well. (Seasons 2–4)
Jordon Elaine Kendall (Joanna Gleason): Leo McGarry's lawyer during the Bartlet MS hearings and love interest for several months (season 3–4)
Tabatha Fortis (Laura Dern): United States Poet Laureate (season 3.16)
Alana Waterman (Lee Garlington): Toby Ziegler's attorney, called upon when Toby confesses to the White House leak. (season 7, Garlington also appeared in the pilot episode as a militant anti-abortion activist.)
Jean Paul Pierre Claude Charpentier, Vicomte de Condé de Bourbon (Trent Ford): Zoey Bartlet's French boyfriend. (season 4)
Colin Ayres (Jason Isaacs): Photographer who has a fling with Donna Moss in the episode "Gaza". (season 5–6)
Lt. Colonel Gantry: pilot of Air Force One, heard several times on personal announcements on the plane.
Colonel Jesse Weisskopf (James Morrison): pilot of Air Force One, seen in the episode "Angel Maintenance" (season 4) informing the President on the status of the plane.
Dr. Millicent Griffith (Mary Kay Place): Close family friend of the Bartlets, Ellie's godmother, occasional medical adviser to the President, and President Bartlet's Surgeon General (Ep. 2.15, Ep. 6.08, Ep. 6.09; mentioned in Ep. 2.18)
Reverend Don Butler (Don S. Davis): A conservative televangelist from Virginia, who is a candidate for the Republican Party's nomination for President of the United States in the 2006 election, but is defeated by Arnold Vinick and politely declines Vinick's offer of the Vice President spot because he cannot support Vinick's pro-choice positions.
Bobby Zane (Noah Emmerich): Defense lawyer for a convicted murderer and high school bully of Sam Seaborn. He contacts Sam to persuade the White House to commute his client's death sentence (Ep. 1.14).
Marco (Matthew Modine): A horologist and high school classmate of C. J. Cregg who helps her deal with her father's steady mental decline due to Alzheimer's disease. Appears in the episode "The Long Goodbye" (Ep. 4.13).
Morris Tolliver (Ruben Santiago-Hudson): He was a physician and Navy officer (Captain), who served as a temporary replacement at the position of Physician to the President of the United States. Despite his relatively low rank for the position, Bartlet liked him and Leo McGarry asked him to stay on full-time. Before he could assume the position, however, a plane he was on during a diplomatic mission was shot down over the Middle East, which prompted the President to "overreact" in the next episode "A Proportional Response". Dr. Tolliver was married to Angela and their daughter's name was Cory. The child was named for her great-grandmother, who had been named after her great-aunt, who got it from the first free woman she ever met. Appears in the episode "Post Hoc, Ergo Propter Hoc" (Ep. 1.2).
Steve Atwood (Željko Ivanek): Republican Chief of Staff to Glen Allen Walken when he was Speaker of the House. He follows Walken to the White House when the Speaker resigns from his post to step in for Bartlet as president. Finds himself at odds with Josh Lyman, who accuses Atwood of conspiring with Walken and the Republican Party for pushing their agenda during the presidency. Atwood denies it, citing that he and the party are in awe of Bartlet for his actions under the 25th Amendment (Ep. 5.1, Ep. 5.2).