As a child, Błaszczykowski witnessed a family tragedy which had a major influence on his life. In September 1996, when he was 10 years old, his father stabbed his mother to death. After his father went to prison, he and his older brother, Dawid, were raised by their grandmother. He briefly gave up football, but with the encouragement of his uncle, Jerzy Brzęczek, a former captain of the Polish national football team, he decided to resume training at Raków Częstochowa two months later. Błaszczykowski has credited his successes to his grandmother. He dedicates every goal he scores to his mother and can be seen looking up to the sky during goal celebrations.

Raised in Truskolasy near Częstochowa, Błaszczykowski began training at Raków Częstochowa when he was eight years old. In 2002, at age 16, he joined the youth side of Górnik Zabrze. In early 2003, he joined KS Częstochowa and played in the Polish fourth league until the end of 2004. His uncle, former Poland captain Jerzy Brzęczek, then helped him get a trial at Wisła Kraków, where he impressed then-manager Werner Lička.

Błaszczykowski quickly broke into Wisła’s first team, with his first league appearance coming on 20 March 2005 against Polonia Warsaw. By the end of the season, he was an established part of the starting 11. With Wisła he won the Polish Ekstraklasa title in his debut season, and they were runners-up the following season. Additionally he won Canal+’s “Football Oscar” for the best midfielder in the Polish top division. He was also named to the Ekstraklasa Best XI of the 2006–07 season in the Polish Footballers’ Association voting.

Błaszczykowski debuted for the Poland national football team on 28 March 2006 in a friendly against Saudi Arabia. He did not receive a call up for the 2006 FIFA World Cup due to injury. He scored his first goal for Poland on 22 August 2007 in a friendly against Russia. Błaszczykowski was an important part of Poland’s successful UEFA Euro 2008 qualifying campaign and was named in Poland’s squad for UEFA Euro 2008, but he withdrew due to injury. On 17 November 2010, in a friendly match against Ivory Coast, Błaszczykowski made his debut as captain of the Polish national team.

In February 2007, Błaszczykowski signed a four-year contract with Borussia Dortmund for an undisclosed fee, joining the Bundesliga side in July of that year. He played with the shirt name “Kuba”, a diminutive form of his first name, until 2012. During the 2008–09 season, he was plagued by a torn leg muscle. He was, nevertheless, voted Polish Footballer of the Year in December 2008.

Błaszczykowski married Agata Gołaszewska in June 2010. Their daughter, Oliwia, was born in 2011. Their second daughter, Lena, was born in 2014. He is a devout Roman Catholic, who reads the Bible on a daily basis, prays often, and participates in the “Nie wstydzę się Jezusa” (Polish “I am not ashamed of Jesus”) project.

Błaszczykowski with Borussia Dortmund won the Bundesliga title for two consecutive seasons in 2010–11 and 2011–12. He also won the 2011–12 DFB-Pokal, providing two assists in the final 5–2 victory over Bayern Munich. In July 2012, he was named on UEFA’s 32-man shortlist for the Best Player in Europe award.

Błaszczykowski signed a new contract with Borussia Dortmund on 24 July 2012, keeping him with the German club until 2016. He scored his first goal of the 2012–13 season in the opening round of the DFB-Pokal on 18 August 2012, setting up Marco Reus for Dortmund’s opening goal before netting their second, as the Yellow-Blacks achieved a 3–0 victory at FC Oberneuland. On 25 January 2013, Błaszczykowski scored two goals within the first 21 minutes against 1. FC Nürnberg, sending Dortmund on their way to a 3–0 victory and putting the defending champions within just nine points of league leaders Bayern. In Dortmund’s 3–2 victory over Bayer 04 Leverkusen on 3 February, which moved Dortmund above Leverkusen into second place, he converted a penalty in the ninth minute to put his side up 2–0. He scored Dortmund’s third goal in a 3–0 rout of Shakhtar Donetsk on 5 March, completing a 5–2 aggregate victory over the Ukrainian champions as Dortmund progressed to the quarter-finals of the Champions League. The result meant that the Yellow-Blacks had advanced to the quarter-finals for the first time in 15 years.

On 8 June 2012, in the opening game of UEFA Euro 2012 against Greece, Błaszczykowski assisted Robert Lewandowski’s goal in a 1–1 draw. In the second group stage match against Russia, he scored a long range equalising goal in a 1–1 draw and was named Man of the Match.

On 2 June 2013, Błaszczykowski signed a new contract with Borussia Dortmund, keeping him at the club until 2018. On 27 July 2013, Błaszczykowski won the 2013 DFL-Supercup with Dortmund 4–2 against rivals Bayern Munich. On 26 October 2013, Błaszczykowski scored a goal for Dortmund in the Revierderby against rivals Schalke in a 3–1 win for Dortmund.

Błaszczykowski was Poland’s current top scorer in their 2014 World Cup qualifying campaign with four goals. His first two strikes were from the penalty spot, his first gave Poland an early lead in their opening group game with Montenegro, a match which finished 2–2. His second goal came four days later, again giving Poland the lead in their 2–0 win over Moldova. He did not feature in the 1–1 draw with England due to injury. Błaszczykowski got the assist for Piszczek’s goal in the 3–1 defeat to Ukraine. He did not feature against San Marino four days later due to an injury sustained in the pre-match warm up. On 7 June 2013, he scored his third goal of the qualifying campaign by grabbing the opener against Moldova – a game which finished 1–1. After San Marino scored an equaliser in a qualifying match on 10 September 2013, Błaszczykowski restored the lead just a minute later and Poland went on to win the match 5–1.

On 31 August 2015, Błaszczykowski joined Fiorentina for a season-long loan from Borussia Dortmund.

On 1 August 2016, Błaszczykowski joined VfL Wolfsburg on a three-year contract for a reported fee of €5 million. In January 2019, his contract with Wolfsburg was dissolved.

On 7 February 2019, Błaszczykowski rejoined former club Wisła Kraków on a free transfer.