Marcarelli is a native of North Haven, Connecticut and graduated from North Haven High School. Marcarelli then received his bachelor's degree in English from Fairfield University in 1992 where he was a member of Theatre Fairfield, the resident production company.
A founding member of New York's Mobius Group Productions in 1998, Marcarelli produced and performed in works by Eric Bogosian, Warren Leight, and Richard Nelson. Mobius's production of The Adding Machine, in which he played the lead role, garnered the award for excellence in overall production from the New York International Fringe Festival in 2001; and his 2005 production, Bridezilla Strikes Back! starring Cynthia Silver, which The New York Times called "irresistible," won the Fringe's overall excellence award for outstanding solo show.
Marcarelli is also a founding member of the Table Ten Films production company. He co-wrote the storyline for the 2011 independent film The Green, for which he also wrote the screenplay.
Marcarelli wrote and produced the feature film Clutter, starring Carol Kane and Natasha Lyonne. The film won Best Film at the Harlem International Film Festival and was nominated for the New American Cinema Award in 2013.
In 2002 Marcarelli started appearing as the "Test Man" character in Verizon Wireless commercials, for which Entertainment Weekly named him one of the most intriguing people of 2002. In October 2009, he appeared on The Price Is Right during the showcase sponsored by Verizon Wireless. In February 2011, he revived his role as the Verizon test man in a commercial advertising the release of the iPhone 4 for Verizon.
In April 2011 Marcarelli was informed by email that Verizon was moving in a new direction with their advertising campaign. He remained under contract but would no longer play "Test Man". Marcarelli was glad that he was able to move on from it.
Prior to Verizon, Marcarelli had already appeared in numerous commercials for companies including Old Navy, Merrill Lynch, Dasani, T-Mobile and Heineken. He also performed in industrial and promotional films, and as a voiceover artist for Comedy Central, United Airlines and Aetna Insurance, among others.
As of 2016 Marcarelli is now working as a Sprint spokesman and often refers to his switch from Verizon to Sprint in the commercials in which he appears.
Marcarelli's husband's name is Ryan, who also appeared with Paul in a Sprint ad.
Marcarelli has a twin brother, Matthew, who is a highly decorated firefighter and the current Assistant Chief of Operations at the New Haven Fire Department. Matthew also was a member of the New Haven 20, a group of firefighters who successfully alleged discrimination before the Supreme Court of the United States in the landmark case Ricci v. DeStefano, 557 U.S. 557 (2009).