Leander was born in Calcutta, India, on 17 June 1973 to Vece Paes, a Goan, and, Jennifer Paes, from Calcutta. He was educated at La Martiniere Calcutta, and the St. Xavier's College of the University of Calcutta. His parents were both Sports persons. Vece was a midfielder in the bronze medal-winning Indian field hockey team at the 1972 Munich Olympics. His mother captained the Indian basketball team in the 1980 Asian basketball championship. Paes enrolled with the Britannia Amritraj Tennis Academy in Madras (Chennai) in 1985, where he was coached by Dave O'Meara. The academy played a key role in his early development. Leander earned international fame when he won the 1990 Wimbledon Junior title and rose to no. 1 in the junior world rankings.

Paes started his Davis Cup career in 1990 at the age of 16, when he partnered Zeeshan Ali in doubles to beat the Japanese team in a gruelling five-set encounter. He is considered one of the top Davis cup players for his country, with a record of 89–32 overall, as of July 2015. He played an important role in the Indian Davis cup team that reached the World Group from 1991–1998. He was part of the Indian Davis Cup team that reached the semifinals of the 1993 Davis Cup with wins against Switzerland and France, eventually losing to Australia. In singles, his major wins came against French duo of Arnaud Boetsch and Henri Leconte in Fréjus, France in 1993, Wayne Ferreira in 1994, and Goran Ivanišević in 1995 when India defeated Croatia, Jan Siemerink in 1995 to defeat Netherlands, and Jiří Novák in 1997. He teamed up with Bhupathi to beat Hirszon and Ivanisevic of Croatia in 1995, Martin Damm and Petr Korda of the Czech Republic in 1997, Nicolás Massú and Marcelo Ríos of Chile in 1997, Broad and Tim Henman in 1998, and Simon Aspelin and Jonas Björkman of Sweden in 2005. In 2007, Leander has three wins (two doubles and one singles) and no losses in the Davis Cup.

Paes first won titles at the Junior US Open and the Junior Wimbledon and he turned professional in 1991. He rose to the number 1 in the world junior rankings. In 1992, he reached the quarter finals of the doubles event in the 1992 Barcelona Olympics with Ramesh Krishnan.

In 1993, ranked No. 197, he lost to No. 238 Fernon Wibierin the first round of qualifying at Wimbledon. Three weeks later he beat No. 25 Arnaud Boetsch on clay in straight sets in the Davis Cup. He also defeated Henri Leconte in the same week and even though Ramesh Krishnan closed the tie out by beating Rodolphe Gilbert in a five-setter, the Architect of that victory was Paes.

In 1994, ranked No 143, he lost in the first round of a Challenger to No 208 Louis Gloria. Four weeks later, he beat World No. 13 Wayne Ferreira in straight sets in the Davis Cup.

In 1995, ranked No 130, he managed to beat Croatia's World No 7 Goran Ivanišević (1992 and 1994 Wimbledon singles finalist) in a controversial five-setter on grass. Jan Siemerink, in 1996, then ranked No. 20, also fell to Paes in the Davis Cup.

He went one better at the 1996 Atlanta Olympics, where he beat Fernando Meligeni to win the bronze medal, thus becoming the first Indian to win an individual medal since KD Jadhav won bronze at the 1952 Helsinki Olympics more than four decades earlier. Paes cited the match as one of his greatest performances on the court, in part because his wrist was severely injured. He was awarded the highest sporting honour by the government of India, the Rajiv Gandhi Khel Ratna in 1996. His first successful year in the ATP circuit came in 1993, when he partnered Sébastien Lareau to reach the US Open doubles semifinal. After having a moderate season in 1994, he reached the quarter-finals of the 1995 Australian Open doubles with Kevin Ullyett. From 1996, he partnered with fellow-Indian Mahesh Bhupathi, which would prove to be a winning combination. Their first year was not a very successful one, especially in the Grand Slams, with a round of 32 finish at Wimbledon being the best. 1997 proved to be a much better year for the team of Paes and Bhupathi, with the semifinals of the US Open their best Grand Slam result. Paes climbed the doubles ranking from no. 89 at the beginning of the year to no. 14 at the end of the year. That year he also made his best singles performance in a Grand Slam, getting to the third round of the 1997 US Open, beating Carlos Costa and Arnaud Boetsch before losing to Cédric Pioline.

Paes played at the year-end championships with Bhupathi from 1997–2000 and in 2002, reaching three finals. In 1997, they lost the final to Rick Leach and Jonathan Stark. They lost the 1999 final to Sébastien Lareau and Alex O'Brien. In 2000, they lost the final to Donald Johnson and Pieter Norval.

The doubles team of Paes and Bhupathi grew stronger in 1998, reaching the semifinals of three Grand Slams, the Australian Open, the French Open, and the US Open. In the same year, Paes had two of his biggest singles results in the ATP tour. The first one came by winning his only ATP singles title at Newport, and the second was beating Pete Sampras, 6–3, 6–4, at the New Haven ATP tournament in the only meeting in their career. In 1999, the duo reached the finals of all four Grand Slams, winning Wimbledon and the French Open, thus becoming the first Indian pair to win a doubles event at a Grand Slam. Paes also teamed up with Lisa Raymond to win the mixed doubles event at Wimbledon. The year also marked his ascent to the no. 1 ranking in doubles. The following year, Paes partnered with Sébastien Lareau for the Australian Open and Jan Siemerink for the French Open, losing in the first round on both occasions. Paes teamed up again with Bhupathi for the US Open, but lost in the first round again. The duo had a disappointing second round exit to Australian duo of Todd Woodbridge and Mark Woodforde at the Sydney Olympics, despite high hopes. Paes was given the honour of carrying the Indian Flag at the opening ceremony of the Sydney Olympics. In spite of a winning the French Open in 2001, the team of Bhupathi and Paes had first-round exits in the other three Grand Slams. Paes was awarded the Padmashri by the Government of India in 2001. The duo of Paes and Bhupathi won the gold medal at the 2002 Asian Games in Busan. In 2002, Leander paired up with Michael Hill for a number of tournaments, with moderate success.

He has won eight doubles and ten mixed doubles Grand Slam titles, and is the oldest man to have won a Grand Slam title. He holds a career Grand Slam in men's doubles and mixed doubles, and achieved the rare men's doubles/mixed doubles double at the 1999 Wimbledon tournament. His mixed doubles Wimbledon title in 2010 made him the second man (after Rod Laver) to win Wimbledon titles in three decades.

Between 2003 and the present, Paes has increasingly focused on his doubles and mixed doubles game. Leander won the mixed doubles events at the Australian Open and Wimbledon with Martina Navratilova, both in 2003. Weeks after the win at Wimbledon, Paes was admitted to the MD Anderson Cancer Center for a suspected brain tumour that was later found to be neurocysticercosis, a parasitic brain infection. While being treated, he had to miss the US Open, but he recovered by the end of that year. In the 2004 Athens Olympic Games, he paired up with Bhupathi, failing again at the semifinals stage. His next Grand Slam success was in the US Open doubles event in 2006 with Martin Damm. Paes led the Indian tennis team at the Doha Asian Games in 2006 and won two golds in the men's doubles (partnering Bhupathi) and mixed doubles (partnering Sania Mirza). Paes maintained his doubles ranking in the top 20 in the world between 2005 and 2007. With wins in the Rotterdam and Indian Wells, Paes took his doubles tally to 38.

Paes is a direct descendant of the 19th century Bengali poet Michael Madhusudan Dutta through his mother. Paes had a live-in-relationship with Rhea Pillai in 2005. The couple have a daughter, Aiyana. She has filed a case at a local metropolitan court against Paes in 2014, alleging that he had her belongings removed from a wing of his home so his visiting parents could stay there.

Paes and Bhupathi took part in the men's doubles at the 2008 Beijing Olympics. They were eliminated in the quarter-finals by Roger Federer and Stanislas Wawrinka, who went on to win the men's doubles gold medal. Later in 2008, with Cara Black, he won the 2008 US Open mixed double title.

In 2009, he won the French Open and US Open Men's doubles titles with Lukáš Dlouhý and was the runner-up in mixed doubles at the US Open.

He began the 2010 season in good form, again winning the Australian Open mixed doubles title with Cara Black. This was the pair's third consecutive Grand Slam final and the fourth overall

In 2011, the "Indian Express" pair won the doubles title at Chennai Open. They reunited to play in a Grand Slam Tournament after nine years and claimed runners-up in the 2011 Australian Open and reached the semifinals in the year-end championships.

Leander Paes was paired with Vishnu Vardhan at the London Olympics 2012, following the refusal of Mahesh Bhupathi and Rohan Bopanna to play with him at the Olympics. Paes threatened to withdraw from the Olympics rather than play with Vardhan, whose world ranking was 296, but withdrew the threat a week later. Paes and Vardhan reached the second round of the tournament, losing to eventual silver medalists Michaël Llodra and Jo-Wilfried Tsonga of France.

The duo has the longest doubles streak in Davis Cup history.
(24 consecutive wins, total 25–2)

Paes won the 2014 Malaysian Open men's doubles with Marcin Matkowski.

On 12 September 2015, Paes won the mixed doubles at the 2015 US Open partnering Martina Hingis, defeating Sam Querrey and Bethanie Mattek-Sands in three sets.

On 3 June 2016, Paes completed his Career Grand Slam in mixed doubles tennis by winning the 2016 French Open with Martina Hingis, thus joining an elite league of players to do so. He also broke Owen Davidson's record for most such titles in gentlemen's section. Paes qualified for the 2016 Summer Olympics in Men's Doubles, and partnered with Rohan Bopanna. They lost in the first round to the Polish pair of Marcin Matkowski and Łukasz Kubot. He later paired up with Andre Begemann, where they reached the final in the Winston-Salem Open. This pair lost in the first round of 2016 US Open. He turned up for the Davis cup against Spain with Saketh Myneni and this pair lost to Rafael Nadal and Marc López in 4 sets.

Paes played in the 2017 season with his 111th partner, Andre Sa. The duo lost to the Indian pair of Purav Raja and Divij Sharan in the first round of Aircel Chennai Open in straight sets. With this loss, Paes moved down to the 64th rank in doubles. Though India won their Davis Cup tie against New Zealand, Paes and his last minute partner, Vishnu Vardhan, lost to the New Zealand pair of Artem Sitak and Michael Venus. Paes and Rohan Bopanna were kept as reserves by new, non-playing captain Mahesh Bhupathi for the tie against Uzbekistan. Eventually, Paes was dropped from final four, which created controversy. Paes reached the semis of the Dubai Open and at Delray Beach. Paes, with Adil Shamasdin, won the Leon Challenger in Mexico. With this victory, he moved to 53rd in the doubles rankings. He then paired with Scott Lipsky and won the Tallahassee Challenger title to move to 49th in the rankings. Paes and Shamasdin won the Aegon Ilkley Challenger, and Paes moved to 62nd in the rankings.Paes and Purav Raja won the 2017 Knoxville Challenger.With this victory Paes moved to 67th in the rankings.Paes and Purav Raja won the 2017 JSM Challenger of Champaign.With this victory Paes moved to 63rd in the rankings and finished off his 2017 season.

Current through the 2018 Davis Cup Z1 2nd round.