Career
Panionios
He started his professional career in 2005 with Panionios, but he failed to make a single appearance for the club, and he was loaned to Fostiras and Pierikos. Iraklis
In summer 2007 he signed for Iraklis, where he was established as a starting left-back by his then-coach, Ángel Pedraza. He made a total of 55 appearances in the Greek Superleague for the team
Köln
In May 2010 he signed for Bundesliga side 1.
Football Club Kölane Koeln have been quick to indicate their contentment with this deal. "We are very glad to have signed Konstantinos Giannoulis, who will be a gain for the defence," said general manager Michael Meier to the club’s official website.
"He fits exactly our left back requirements for the coming season." Kicker reports that because of Iraklis ongoing financial difficulties, Koeln have been able to swoop for the defender by tabling a “low six-figure fee”. They were not the only German outfit interested in the full-back, as Kaiserslautern had already made concrete steps towards securing the Greek’s signature.
After half a season however, having never played for the first team, he was told that he could leave the club for free.
Atromitos
On 23 June 2011, he agreed to sign a season-long loan deal with Greek Superleague side Atromitos, where he made 25 appearances and scored 1 goal. On 7 August 2012, Giannoulis was officially released by 1. Football Club Köln and subsequently signed a three-year contract with Atromitos.
On 28 June 2014, the 27 years old defender signed an extension of his contract (which ended at 2015) for another two years in presence of the Technical Director Mr.
Giannis Aggelopoulos. He is the seventh football player that in a period less of a year that renews his contract with our team after Tasos Karamanos, Luigi Cennamo, Nikolaos Lazaridis, Efstathios Tavlaridis, Luiz Eduardo Santana Brito and Miguel Sebastián Garcia.
Kostas Giannoulis a football player with ethics, quality and inexhaustible source of strength had the last season (2013/14) 44 appearances in all the organizations. Olympiacos
On 31 August 2014 it was announced that Kostas Giannoulis has joined Olympiacos.
Giannoulis commented the following at atromitosfc.gr: "A great thank is nothing in front what I owe to Atromitos.
On 9 July 2015, he solved his contract with the club Asteras Tripoli
On 15 July 2015 it was announced that Kostas Giannoulis has joined Asteras Tripoli on a two years" contract for an undisclosed fee. He made his international debut for Greece on 15 November 2011, in a friendly match against Romania.
Olympiacos
Superleague Greece: 2014-2015
Greek Cup: 2014-2015.