Nesta was raised in the Cinecittà area of Rome. He attended the Margherita Bosco primary school where he first started playing football. His older brother, Fernando, was advised to play a sport because of a back problem and enrolled at the local football club. Alessandro threw a tantrum until his father gave in and enrolled him as well, thus marking the beginning of his career.
Nesta's talent was first discovered by Francesco Rocca, then a scout for Roma, but Nesta's father, a Lazio fan, turned down the offer. In 1985, he joined Lazio's youth academy, where he rose through the ranks playing in various positions, including striker and midfielder, before settling in defence. His international career first showed signs of growth when he played for Italy's under-15 and under-16 sides. He was promoted to Lazio's senior squad in 1993, and first came to the attention of fans for being involved in a training ground accident that broke teammate Paul Gascoigne's leg.
He assumed the team captaincy in 1997, and helped Lazio win the 1998 Coppa Italia after beating Milan in the final, in which he scored the winning goal. This was followed by a UEFA Cup Winners' Cup and European Super Cup in 1999, and a rare Scudetto and Coppa Italia double in the 1999–00 season, in addition to two Italian Super Cups.
Alessandro Nesta began his career for Italy was a member of the Under-21 squad that won the 1996 UEFA European Under-21 Football Championship. A few months later he was named to Italy's Euro 96 squad in England but did not come off the bench as Italy was eliminated in the group stage by eventual finalists Germany and Czech Republic. He earned his first cap for the Azzurri in a World Cup qualifier against Moldova on October 5, 1996.[7] He made seven appearances in the qualifying campaign and was included in the final squad. At the 1998 FIFA World Cup, Nesta appeared in all three group games but made no further appearances due to injury. Two years later, Nesta featured at UEFA Euro 2000 partnering Paolo Maldini and Fabio Cannavaro in defense throughout most of the tournament as Italy reached the final.
Following Euro 2000, Nesta appeared regularly for the Azzuri as a first choice center back under Giovanni Trappatoni. During the 2002 FIFA World Cup, Nesta partnered Fabio Cannavaro in central defense but once again injury kept him out of the second round defeat to Korea.[8] Italy's disappointment continued at UEFA Euro 2004 as they were eliminated in the first round by Denmark and Sweden. Nesta started in all three games partnering Cannavaro and later Marco Materazzi. Following two successive disappointments, newly appointed manager Marcello Lippi kept Nesta in the lineup as a starter. Nesta appeared consistently as Italy topped their qualification group with seven wins, two draws, and one loss. In the 2006 FIFA World Cup final tournament, Nesta was once again a starter, however injury the final group game against the Czech Republic put him on the sidelines as Italy went on to win the trophy.[9] After the World Cup, Nesta made one appearance in the Euro 2008 qualifiers against Georgia but his continuous injuries forced him to retire from the international team.[10] Prior to the final tournament, Nesta declined Roberto Donadoni's invitation to return to the national team.[11] Two years later, he similarly turned down an invitation from Marcello Lippi prior to the 2010 FIFA World Cup.
On 7 May 2007, Nesta married his fiancée, Gabriela Pagnozzi, in a civil ceremony in Milan; the religious ceremony followed on May 30, 2007. Gabriela was working for Casa Italia, the Italian national team HQ, during the 1998 World Cup. Their relationship was born when she tended to him following his injury against Austria. "I can say, I got the injury and her in France then. And the injury has gone, [but] she has stayed with me." Their daughter, Sofia, was born on October 19, 2006 and on March 20, 2008 their son Tommaso was born.