Lanzi began racing in 1996 at the age of 15 in the Italian 125 Sport class. Two years later he won that title and moved up to 125 GP competition in the Italian and European championships. In 2001 he attempted a step up to 250 GP but the season was unsuccessful, and he stepped away from racing for a year in 2002.
In 2003 Lanzi returned to competition with Rox Ducati in the FIM Superstock 1000 Cup, losing the title by only three points — a near-miss that nonetheless confirmed his capability on large-capacity machinery. The following year he moved into the Supersport World Championship with Ducati Breil, finishing fifth overall.
Lanzi joined the Caracchi Ducati team for the 2005 Superbike World Championship season. His start was disrupted by a poor opening stretch and injury that kept him out of two rounds. However, a run of eight successive top-ten finishes brought him to the attention of the factory team, and at the EuroSpeedway Lausitz round he was drafted into the Xerox-sponsored factory Ducati squad as a substitute for the injured Régis Laconi.
Lanzi qualified on pole position for both races. Race one was compromised when he overshot the first corner and took an escape road, cutting several sections of the circuit in the process. He rejoined in third but received a mandatory ride-through penalty, working back through the field to finish eighth. Race two delivered the result his form had suggested was possible: Lanzi won ahead of Chris Vermeulen and Noriyuki Haga. He secured a second Superbike victory later that season at Magny-Cours, ending the year as a rider who had earned a factory place.
Lanzi's 2005 results earned him a full-season berth on the factory Ducati for 2006 alongside Troy Bayliss, who dominated the championship that year. Lanzi did not win a race during the campaign and finished eighth overall, often finding himself behind Ruben Xaus, who was riding a year-old 2006-specification machine from a separate team.
Lanzi remained with the factory team in 2007 but again found himself in Bayliss's shadow, and Xaus again outpaced him at times on the older specification bike. The season produced no race wins and further underlined the difficulty of converting qualifying and one-off pace into consistent championship results.
Dropped by the factory team for 2008, Lanzi continued riding a Ducati with Team RG. He took his third and final World Superbike victory at Valencia in race one, overtaking Troy Bayliss for third on the final lap in unusual circumstances — the riders ahead of him, Max Neukirchner and Carlos Checa, collided while disputing the lead, handing Lanzi the win. It was his only top-five finish of the season, and he ended the year fourteenth overall.
Following his World Superbike seasons, Lanzi continued competing in Italian domestic championships, including the CIV Superbike Championship, where he has raced aboard a BMW S1000RR.
Lanzi's career is defined by his 2005 Lausitz win — a substitute appearance on a factory Ducati in which he qualified on pole and converted race two into a first World Superbike victory despite a penalty undoing his race-one chance. His three career wins across competitive seasons marked him as a rider capable of peak results when circumstances aligned, even if sustained championship contention remained out of reach.