Bosco was born in Jersey City, New Jersey, the son of Margaret Raymond (née Thek), a policewoman, and Philip Lupo Bosco, a carnival worker. His father was of Italian descent and his mother was of German ancestry. Bosco attended St. Peter's Preparatory School in Jersey City, and later studied Drama at Catholic University of America, where he had notable success in the title role of Shakespeare's Richard III.
Bosco married a fellow Catholic University student, Nancy Ann Dunkle, on January 2, 1957. They have seven children, Jenny, Diane, Philip, Chris, John, Lisa, Celia and 15 grandchildren. In recent years Mr. Bosco has been battling Alzheimer's disease, effectively ending the New Jersey native's acting career in 2010. Bosco currently resides in Haworth, New Jersey.
Bosco began his career in Broadway theatre. He received a Tony Award nomination for his debut in The Rape of the Belt in 1960 and spent the next three decades supporting major stars in classic revivals like Cyrano de Bergerac, King Lear, and Twelfth Night.
He appeared in revivals of plays by George Bernard Shaw, including Man and Superman, Saint Joan, Mrs. Warren's Profession, Major Barbara, Heartbreak House (opposite Rex Harrison), and You Never Can Tell, winning Tony nominations for the last three. He also appeared with Shirley Knight in the Roundabout Theatre Company revival of Come Back, Little Sheba.
Following his Tony-winning performance in the farce Lend Me a Tenor in 1990, Bosco appeared on Broadway in An Inspector Calls (1994), The Heiress (1995), Twelfth Night (1998), Copenhagen (2000), and Twelve Angry Men (2004).
He played "Grandpa Potts" in the 2005 Broadway production of Chitty Chitty Bang Bang, and capped his Shawian work as the aged Captain Shotover in a Broadway revival of Heartbreak House in 2006. He retired from the stage in 2009, after appearing in the City Center Encores production of Finian's Rainbow, although he loaned his voice to Douglas Carter Beane's 2010 play "Mr. and Mrs. Fitch".
Bosco has appeared regularly in the Law & Order franchise of television series, in various roles ranging from judges to lawyers to villains. (He is perhaps known for his role of Judge Joseph Terhune on Law & Order: Special Victims Unit). His film credits include Hogan's Goat, Working Girl, Children of a Lesser God, Walls of Glass, Straight Talk, Nobody's Fool, Wonder Boys, The Money Pit, Three Men and a Baby, Milk Money, Quick Change, Angie, The First Wives Club and The Savages.
Bosco narrated the 1991 documentary film Coney Island, directed by Ric Burns and did the voice of a number of characters for his brother Ken's documentaries for PBS. Bosco also portrayed Vincenzo the butler in the 1995 comedy It Takes Two, and portrayed Walter Wallace, father of the bride-to-be in the 1997 romantic comedy My Best Friend's Wedding, co-starring Julia Roberts, Cameron Diaz and Dermot Mulroney.
In 1988, Bosco won a Daytime Emmy award for his appearance in the ABC Weekend Special 'Read Between The Lines'. Bosco was a series regular on the FX original series Damages. He read Desert Giant: The World of the Saguaro Cactus by Barbara Bash as its narrator on the PBS series Reading Rainbow in its sixty-second episode on March 27, 1990. In 1998, Bosco was inducted into the American Theater Hall of Fame.