Born July 26, 1965 in New York, but raised in Chicago, Piven was the son of Byrne and Joyce Piven, founders of the Piven Theatre Workshop – a company which would go on to nurture John and Joan Cusack, Rosanna Arquette and Aidan Quinn. Acting from childhood, he would later become a member of the Second City National Touring Company, a pivotal bit of comic training that would serve the young actor well later on in his career. Moving from the stage, Piven segued to features as one of the bullying jocks in "Lucas" (1986). His subsequent work included playing one of the Gas 'N Sip boys in Cameron Crowe's classic, "Say Anything" (1989) – a film that starred Piven's childhood pal John Cusack – a sailor who gets duped by Cusack in Stephen Frears' "The Grifters" (1990), and one of the devoted fanatics in "Bob Roberts" (1992).

With his career definitely on an upswing, Piven landed small roles in big films such as "White Palace" (1990), "Singles" (1992), and "Miami Rhapsody" and "Heat" (both in 1995). Just as importantly, Piven also began netting larger roles in smaller films, including "The Player" (1992), the romance "Twogether" (1992), the action flick "Judgment Night" (1993), and the troubled comedies "Car 54, Where Are You?" (1994) and "Dr. Jekyll and Ms. Hyde" (1995). His first starring role was as a trouble-making college student in the low-budget, boisterous "PCU" (1994), followed by another lead in the Oxford-set romance "E=mc2" (1995), and a turn as a writer romancing movie star Sherilyn Fenn in "Just Write" (1997). All good resume-building experience, but nothing earth-shaking for his career.

Making the right move at that time, Piven jumped to television, appearing as a stock player on Carol Burnett's short-lived variety series, "Carol & Company" (NBC, 1990-91), and making guest appearances on such shows as "Seinfeld" (NBC, 1990-98) and "Chicago Hope" (CBS, 1994-2000). But it was his 1992-93 stint on HBO's "The Larry Sanders Show" (HBO, 1992-98), which brought him his first real notice. As Jerry Capen, the over-the-top writer on the fictitious late-night talk show, Piven went all-out in hilariously portraying Capen’s personal life meltdown, brought on by abuse of sex and drugs, until he was finally fired. He mastered that character to such an extent that he made a 180-degree turn back to normalcy with his roles as an out-of-work dad on the short-lived sitcom "Pride and Joy" (NBC, 1995) and in the TV-movie thriller "12:01" (Fox, 1993).

In 1995, he reclaimed a bit of his “Larry Sanders” bravado by appearing as Ellen DeGeneres' grating and obnoxious cousin, Spence Kovak (replacing the male lead vacated by Arye Gross), on the comedienne’s successful sitcom, “Ellen” (ABC, 1994-98). After the show was cancelled, following the “outing” of DeGeneres’ TV character, and a consequent massive ratings dive, Piven returned to series TV more than once in the late 1990s, starring in a pair of short lived, lighthearted ABC dramas, "Cupid" (1998) – in which he played a man who believed himself to be the Greek god of love – and "Partners" (1999).

Despite making a mark on both small and big screens, Piven still found time for stage work, co-founding with childhood friend Cusack, the Chicago-based theater company, New Criminals. The experimental company allowed the actor to push the envelope, with him later going so far as to say, "unless an entire row of people got up in the middle of a performance and leave the theater in disgust, I feel as though I haven't done my job.” Piven's real-life friendship with Cusack continued to prove fruitful, as he became the then bigger star’s preferred sidekick/foil in several films, especially those which Cusack produced himself. The witty team demonstrated their considerable “buddy-buddy” chemistry in the ultra-quirky but endearing hit man-goes-home-for-high school-reunion comedy, "Gross Pointe Blank" (1997), in which Piven played hit man Cusack's teen crony-turned-dentist Paul. The two actors re-teamed in the romantic comedy "Serendipity" (2001), with Piven's best friend character helping Cusack pursue the woman he may have been fated to fall in love with (Kate Beckinsale). The Chicago boys were both featured in the film adaptation of author John Grisham's legal potboiler "Runaway Jury" (2003), with Piven as a shrewd but inexperienced jury consultant.

Even without Cusack, Piven began carving out a solid niche as a supporting player and character actor – usually playing a variation of his oily, comedic persona – but sometimes in straight dramatic roles as well, including the feature films "Kiss the Girls" (1997), the HBO biopic "Don King: Only In America" (1998), "Very Bad Things" (1998), "The Family Man" (2000), "Rush Hour 2" (2001) and "Black Hawk Down" (2001). In 2003, Piven made the most of an underwritten role as the comic villain in the hit comedy "Old School," playing the dastardly, wound-too-tight college dean who attempts to thwart with comic verve, the fraternity created by three middle-aged men – Luke Wilson, Will Farrell and Vince Vaughn. Indeed, with his portrayal of Dean Gordon “Cheese” Pritchard, Piven seemed to pay tribute to such archetypal characters created in the late 1970s and early ‘80s by actors such as "Animal House's" John Vernon (Dean Wormer). That same year he also landed a brief role as a bland newscaster in "Scary Movie 3," and the following year, played a Secret Service agent caught up in a romantic subplot in the vacuous Mandy Moore film, "Chasing Liberty" (2004).

Thankfully for Piven, after playing second banana for so long, the actor scored his biggest role to date when the HBO series, “Entourage” debuted in 2004. Although not a member of the 4-man group of the show’s title, he grabbed audiences and would not let go with his hilarious, dead-on performance as the morally challenged, hard-driving, ultra-abusive talent agent Ari Gold. His comment, "Hug it out, b*tch!" became a buzz-phrase heard not only in agency hallways and power lunch spots in L.A., but across the country too, as audiences began to get hip to the show’s brilliance with each passing season. Piven was such a stand-out, he earned a Golden Globe nomination for Best Performance by an Actor in a Supporting Role in a Series, MiniSeries or TV Movie and an Emmy nomination as Outstanding Supporting Actor in a Comedy Series, both in 2005. Though he was passed over for both that year, Piven finally received his well-deserved “Entourage” Emmy in 2006 for Best Supporting Actor in a Comedy Series. With his mother by his side, the man whom many felt had been robbed the year before, dashed up to the stage, thanking his mom and, holding the award aloft with a kiss, thanked his late father as well for nurturing his childhood dream of becoming a respected actor. On Sept. 16, 2007, Piven received his second consecutive Emmy win in the same category, this time going up against “Entourage” co-star Kevin Dillon, who was also nominated for his role as Vincent Chase’s devoted brother and perennial hanger-on, Johnny “Drama” Chase. And with the ball still rolling, Piven surprised by winning another Golden Globe in early 2008 for Best Supporting Actor in a Series, Miniseries or TV Movie for his continued craziness on "Entourage."