He is the son of Eva Janko, who won a bronze medal in the women's Javelin event at the 1968 Summer Olympics in Mexico City.

[citation needed] Janko scored five hat tricks in the league during the season, including a four-goal performance after coming on as a second-half substitute against SCR Altach in a 4–3 victory.

His best performances were a four-goal effort against FC Kärnten on 4 October, and a pair of goals scored against Josko Ried on 13 February 2010.

[2] Janko was also an integral part of the Salzburg team that enjoyed success in its pool play in the UEFA Europa League.

[citation needed] He had a strong performance against Standard Liège on 19 February 2010, scoring his side's two goals in a 3–2 loss in the first tie of the round of 32.

[3] Janko signed a four-year contract with Dutch club Twente on 21 June 2010 and was given the number 21 shirt, previously worn by fellow Austrian Marko Arnautović.

[9][10][11] In the 2011 Johan Cruyff Shield on 30 July 2011, Janko scored from the penalty-spot as Twente defeated reigning Eredivisie champions Ajax 2–1 to lift the cup.

[14] On 29 September, he scored twice to lead Twente to a first victory in the UEFA Europa League, a comfortable 4–1 win over Wisła Kraków.

[18] On 31 January, Janko was officially unveiled as a Porto player and was given the number 29 shirt, joining in a €3 million move and signing a contract until June 2015.

On 28 August 2012, after just half a year at Porto, Janko signed for Turkish club Trabzonspor for a €2.4 million transfer fee.

[26] On 31 July 2014, Janko was announced as Sydney FC's new marquee signing for the 2014–15 A-League season,[27] on a one-year deal, meaning his wages were permitted to be paid outside the league's salary cap.

On 30 August, he scored his first goal for Sydney during the final of the inaugural Townsville Football Cup in a 2–0 win against Brisbane Roar.

[29] Janko scored his next two goals in the form of a brace against Melbourne City, after having turned down the opportunity to play for the Austria national team against Brazil.

[31] Janko scored his first hat-trick for Sydney in their 5–4 win against Brisbane Roar on matchday 21 at Allianz Stadium in rather inclement conditions.

[34] On 25 June 2015, it was announced that Janko joined Swiss side Basel on a free transfer, signing a one-year deal, with an option for a furtheryear.

[40] At the start of the 2016–17 Super League season, FCB strengthened their attacking formation, signing Ivorian player Seydou Doumbia from AS Roma.

[46] Janko made his debut for Austria in a May 2006 friendly match against Croatia and earned his second cap in October that year against Liechtenstein.