[4] Having finished as runner-up at two junior major tournaments, Janowicz rose to prominence on the pro circuit leading up to and following his run to the final, as a qualifier, of the 2012 Paris Masters, during which he defeated five top-20 players such as Andy Murray and Janko Tipsarević.

Despite losing to David Ferrer in the finals, he made his top-30 debut in the ATP rankings and became the highest-ranked male Polish tennis player.

[8] Every October Janowicz and his team run the annual Atlas Jerzyk Cup tennis tournament in Łódź, Poland promoting the sport to young children, ages 8 to 12 years old.

He was the first qualifier to do this since Andrei Pavel in 2003 and the first player to reach the final on his ATP World Tour Masters 1000 debut since Harel Levy in 2000.

He won his first two matches against Simone Bolelli in straight sets, and Somdev Devvarman of India, against whom he had to recover from a two-set deficit to win in five.

He continued to play at the Madrid Masters, where he won his first-round match against Sam Querrey, but was eliminated in the second round by eventual semifinalist, Tomáš Berdych.

He then played at the Italian Open, where he reached the quarterfinals with consecutive wins over two top-ten players, Richard Gasquet and Jo-Wilfried Tsonga.

He then beat fellow Pole Łukasz Kubot in straight sets, becoming the first Polish man to reach a Grand Slam semifinal.

[17] He did not reach quarterfinals in his next few tournaments, falling to Fernando Verdasco by retirement in Hamburg Open and Rafael Nadal in two tight sets at the Rogers Cup.

He returned in October to reach the quarterfinals at the Stockholm Open, where he lost to Ernests Gulbis in three sets, a player he had beaten in the previous year's Wimbledon in a long five-set match.

He won his opening meeting with Santiago Giraldo, but did not defend points due to his loss to top seed Rafael Nadal.

Janowicz was to partner Agnieszka Radwańska in the Hopman Cup, the annual international mixed-team tournament in Perth, Western Australia, but was unable to do so due to a foot injury.

Janowicz was due to play at Open 13 in Marseille, where he made it to the previous year's quarterfinals, but withdrew from the event to recover from a case of sinusitis.

Similarly, he was defeated by Roberto Bautista Agut in the second round at the Sony Open Tennis ATP World Tour Masters 1000 in Miami.

Additionally, he made an early exit at the Monte Carlo Rolex Masters, where he failed to make it past the first round, going down in straight sets against the French veteran Michaël Llodra.

Following Wimbledon, Janowicz competed at the Swedish Open in Båstad, where he was forced to retire in the first round due to a left foot injury.

Janowicz began his US Open Series campaign at the Rogers Cup in Toronto, where he fell to Canadian wildcard Peter Polansky.

After Cincinnati, Janowicz continued at Winston-Salem Open, where he defeated Carlos Berlocq, João Sousa, Édouard Roger-Vasselin, David Goffin, and Sam Querrey, then lost to Lukáš Rosol in the final despite having two championship points in the third set.

Janowicz and Radwańska claimed their first Hopman Cup title after they beat the top-seeded USA team 2–1 in a final mixed doubles match over the Americans Serena Williams and John Isner.

Janowicz continued at Open Sud de France in Montpellier where he defeated Dustin Brown, Benoît Paire, Gilles Simon and João Sousa to make his third ATP final.

The following week Janowicz defeated Édouard Roger-Vasselin and Roberto Bautista Agut, then lost to David Goffin in the third round of the Miami Masters.

Janowicz started the grass season with the Stuttgart Open tournament, where he defeated Dustin Brown, then lost to Philipp Kohlschreiber in the second round.

Janowicz continued at the German Open Tennis Championships in Hamburg where he defeated Taro Daniel, then lost to Pablo Cuevas in three sets.

In March, Janowicz was originally expected to play Poland's first Davis Cup World Group tie, but two days before the event he had to undergo tests on his injured knee.

[23] In July Janowicz participated at the Open Castilla y León ATP Challenger Tournament in Segovia, Spain, where he lost to Luca Vanni in the first round.

[24] In August, Janowicz competed at the 2016 Summer Olympics in Rio de Janeiro, Brazil, where he lost to Gilles Müller in the first round.

Next Janowicz made a winning start to Slovak Open, a Challenger event in Bratislava, defeating Norbert Gombos and Bernard Tomic, then lost to Mikhail Kukushkin in the quarterfinals.

[32][33][34] In 2009, Janowicz played a major role in Poland's 3–2 Davis Cup win over Great Britain at Liverpool's Echo Arena.

In 2013 Jerzy Janowicz won the decisive fourth rubber for Poland with Slovenia to secure a Europe/Africa Zone Group I second-round tie against South Africa.

[35] Janowicz also moves remarkably well considering how big he is, and hits powerful groundstrokes from the back of the court and has an excellent drop shot.