|Date of birth||20 March 1988|
|Place of birth||Trutnov, Czechoslovakia|
|Height||1.81 m (5 ft 11 in)|
|1999–2000||SK Hradec Králové|
|2002–2005||FC Slovan Liberec|
|2005–||FC Slovan Liberec||93||(23)|
|2008||→ SK Slavia Prague (loan)||7||(1)|
|2008–2011||→ Larissa (loan)||35||(3)|
|2011–2012||→ SK Slavia Prague (loan)||14||(2)|
|2013–2014||→ Apollon Smyrni (loan)||5||(0)|
|2014||→ Podbeskidzie Bielsko-Biała (loan)||5||(1)|
|2014||→ Aiginiakos (loan)||2||(0)|
|2015||→ Dukla Prague (loan)||8||(0)|
|2015||→ Slavoj Vyšehrad (loan)||0||(0)|
|2004||Czech Republic U-16||3||(1)|
|2004–2005||Czech Republic U-17||16||(10)|
|2005||Czech Republic U-18||1||(0)|
|2005–2007||Czech Republic U-19||18||(6)|
|2006–2008||Czech Republic U-21||5||(0)|
|* Senior club appearances and goals counted for the domestic league only and correct as of 30 June 2015.
‡ National team caps and goals correct as of 15 February 2015
Blažek is known as a very talented as well as a somewhat controversial player, due to his conflicts with coaches and alcohol consumption. On his web site he stated his motto: Děvky, chlast a prcání (hookers, booze and fucking). The site also included many photographs of him drinking rum with cola. After Blažek's transfer to Slavia, the web site gained some attention of the media, resulting in motto being changed to věř v sám sebe (trust in yourself) and the controversial photographs were removed.
In July 2011 Blažek returned to his mother club FC Slovan Liberec. On 24 July 2012, Blažek scored a goal against Kazakhstani club Shakhter Karagandy at the very end of the period of extra time to level the result at 1–1 and enable his team to progress to the next round of the UEFA Champions League by an aggregate score of 2–1. He spent time at Greek second division side Aiginiakos in the autumn part of the 2014–15 season, before joining FK Dukla Prague on loan in February 2015.
On 15 November 2009, Blažek made his first appearance for the national team in a friendly game against United Arab Emirates.
- "Děvky, chlast a …". Blesk (in Czech). 4 January 2008. Retrieved 15 February 2015.
- Jan Blažek's personal profile – in Czech.
- "Útočník Blažek se vrací do ligy, jaro stráví na hostování v Dukle". Mladá fronta DNES (in Czech). 13 February 2015. Retrieved 15 February 2015.