As the on-screen heel cousin of Jamie Noble, he attacked then face Crash Holly after he defeated Noble in a match on the December 12, 2002 edition of SmackDown!. Nunzio began a feud with Holly after this, defeating him on several occasions before going on to face the likes of Tajiri, Shannon Moore, and Chuck Palumbo.
The team and cousin storyline of Nunzio and Noble soon faded. Nunzio formed the Full Blooded Italians, with Johnny "The Bull" Stamboli and Chuck Palumbo, but the team found little success. After WrestleMania XX, Palumbo was drafted to Raw, and the F.B.I. was reduced to a tag team. After Stamboli was released, Nunzio began competing in the cruiserweight division.
In 2005, Nunzio changed his name to Little Guido Maritato for one night; he teamed with the Full Blooded Italians to take on Super Crazy and Tajiri in a three-way dance at the ECW reunion show One Night Stand.
As Nunzio, he continued to perform on SmackDown! B-show Velocity as both a fan favorite and a villain, forming a short-lived tag team with Funaki. On the August 6 (taped on August 2) edition of Velocity, Nunzio won the Cruiserweight Championship by defeating Paul London after a new villainous wrestler, Vito, made his debut by giving Nunzio a blackjack, which he used to knock London out. Nunzio joined forces with Vito, thus becoming a full-time villain.
The pair began feuding with The Mexicools and at No Mercy, Mexicool member Juventud defeated Nunzio with a Juvi Driver to take the Cruiserweight Championship. Nunzio regained the title on November 15 at a house show in Rome, Italy but lost it right back to Juventud on the November 25 SmackDown.
Nunzio and Vito would both briefly turn into fan favorites by briefly engaging in a feud against Gregory Helms. Vito and Nunzio would quickly go back to being villains, however, due to Vito's new godfather gimmick.
In late May 2006, Nunzio's partnership with Vito began to crumble after it was revealed that, in storyline, Vito enjoyed cross-dressing, which made Nunzio feel betrayed and embarrassed. Nunzio ended his alliance with Vito, and moved to the ECW brand.
In June when the ECW brand was launched, Nunzio left SmackDown to join other "ECW originals" on ECW, retaking his Little Guido name in the process. The F.B.I. was revived again, this time with Little Guido as a face once again, alongside Tony Mamaluke and Trinity and for a short while, Big Guido. The F.B.I. were used for tag matches on ECW to either take on debuting tag teams or facing another tag team when a tag match is needed. At December to Dismember, they took on Elijah Burke and Sylvester Terkay in a losing effort. His partner Tony Mamaluke was released on January 18, leaving Guido and Trinity alone to carry on the stable.
After Mamaluke's release, Little Guido vanished from television (he only appeared once on ECW on Sci Fi with the Little Guido name). After his hiatus, he later returned on the April 17, 2007 episode (in Italy, where he was well received by fans) using his old Nunzio name again but without Trinity, who had been released in June. After losses to the debuting Johnny Nitro and The Miz, Nunzio disappeared from television for a few months. He returned on the September 11 edition of ECW, in a losing effort to Matt Striker. Nunzio was used mainly as a jobber during this period, losing to Tommy Dreamer, Jamie Noble, Kevin Thorn, and Kenny Dykstra.
In 2008, Nunzio returned on January 15, in a losing effort against Shelton Benjamin, and on his next appearance, on April 8, he lost to Elijah Burke. He then engaged in a brief feud with Mark Henry, but came out on the losing end. After nearly 2 years, Nunzio finally won a broadcast match on May 5, as he was in a handicap match along with the rest of the ECW roster against Triple H and Mr. Kennedy.
On August 8, 2008, Nunzio was released from his WWE contract.
Nunzio appeared at a house show for WWE Raw, at Madison Square Garden on December 26, 2010, as a referee when the majority of referees could not make it to the arena due to blizzards and gale force winds; this position expanded to televised events on February 1. On September 29, 2011, he announced that he was no longer working for WWE.