Mattila was born in Tampere, but began his senior club career in Helsinki playing for Klubi-04, before making his league debut for HJK at age 18 in 2008.

[1] Before the season 2008, HJK was on a training camp in Marbella and Mattila was spotted by scouts of Sevilla FC and Málaga CF.

[16] Mattila made his Superliga debut on 14 August 2016 in a match against Brøndby when on 64th minute he replaced Adama Guira as a substitute.

[18] He made his debut for the Finland national team on 30 October 2013 in a friendly match in Qualcomm Stadium, San Diego against Mexico.

[19] Mattila earned his second cap for Finland on 5 March 2014, in the 2:1 away win over Hungary in a friendly match after coming on as a last minute substitute for Roman Eremenko.