Gemignani was married in August 2008 to actor/director Erin Ortman.
- John Hinckley in the Roundabout Theatre's Assassins
- Beadle Bamford in the John Doyle's 2005 Broadway revival of Sweeney Todd: The Demon Barber of Fleet Street (Drama Desk Award nomination for Outstanding Featured Actor in a Musical)
- Jean Valjean in the 2006 Broadway revival of Les Misérables
- South Pacific, staged concert with Reba McEntire and Brian Stokes Mitchell at Carnegie Hall in June, 2005
- Passion, with Patti LuPone, Michael Cerveris, and Audra McDonald at The Rose Theater in March 2005
- Sweeney Todd: The Demon Barber of Fleet Street in John Doyle's 2007 national tour of the Broadway production opposite Judy Kaye
- Boatman/Dennis in the 2008 Broadway revival of Sunday in the Park with George
- Addison Mizner in the Sondheim-Weidman 2008 musical Road Show at the Off-Broadway Public Theater
- Moishe Rosenwald in the new musical The People in the Picture at Studio 54 in 2011.
- Nick Merritt in the play Headstrong at Ensemble Studio Theatre in 2012
- Billy Flynn in the Broadway revival of Chicago in 2013.
- Violet's Father in the Broadway Revival of Violet.
- King George III in the Chicago production of Hamilton
- Enoch Snow in the Broadway production of Carousel (Tony and Grammy award nominations) in 2018.
- Alfred P. Doolittle in the Broadway production of My Fair Lady in 2019.
Gemignani participated in a memorable performance of "Opening Doors" from Merrily We Roll Along at Symphony Space's Wall to Wall Sondheim event celebrating Sondheim's 75th birthday in March 2005. He also performed in three gala concerts honoring Sondheim's 80th birthday in 2010: with the New York Philharmonic at Avery Fisher Hall, singing "Something's Coming" from West Side Story in March; then at New York City Center in April; and with The New York Pops at Carnegie Hall in November. And he performed "Buddy's Blues" from Follies in the online 90th birthday celebration, "Take Me To The World" on April 26th, 2020. He made his conducting debut with the New York Philharmonic in Live from Lincoln Center's "New Year’s Eve: Celebrating Sondheim" on December 31, 2019.
Recently, Gemignani has begun to work as a music director, following in his father's footsteps. He served as the conductor, music director, and music supervisor for the 2020 revival of West Side Story, and has developed pieces for the Public Theatre and the Roundabout Theatre Company.  He served as music director and orchestrator for the Fiasco Theatre production of Merrily We Roll Along. 
- Kampfe, John. "Tenafly: Small Town, Big Stars – Part 2", Jerseywood, June 13, 2016. Accessed October 9, 2018. "Alexander Gemignani — The son of renowned Broadway music director Paul Gemignani is known primarily for his work on the New York stage.... Gemignani was born in New York City but grew up in Tenafly and, yes, he too is a Tenafly High alum (1997)."
- Hetrick, Adam."Sondheim and Weidman's Road Show Pulls Into the Public Oct. 28" Archived 2008-10-31 at the Wayback Machine, playbill.com, October 28, 2008
- New York City Center Gala Honoring SONDHEIM, BroadwayWorld, April 29, 2010.
- "LIVE FROM LINCOLN CENTER: New York Philharmonic New Year's Eve 2019: Sondheim Celebration". 18 November 2019.
- "Alexander Gemignani".
- "Alexander Gemignani | NYU Steinhardt".