[12] Despite his young age, he was immediately included in the first team and made his debut with a rosanero jersey as a second-half substitute in the first leg of the 2010–11 UEFA Europa League play-off against Maribor.

Following his loan spell with Luzern came to an end, Manager Martin Jol revealed Kasami took a fifty per cent cut of his wage to stay at the club.

Kasami then scored his second goal of the season against Crystal Palace on 21 October; a dipping volley from the edge of the area, in a match that eventually ended a 4–1 away win to Fulham.

[26] On 22 October 2014, Olympiacos pulled off one of the surprises of the Champions League night when they beat Juventus 1–0 in Piraeus with a first-half goal from Kasami.

[29][30] On 11 March 2015, Olympiakos's Portuguese coach Vitor Pereira and Kasami were fined for their behavior after the team's Greek Cup quarter-final 1–0 win over AEK Athens.

The disciplinary committee of the Greek soccer federation fined Pereira €9,000 and Kasami was ordered to pay €7,000 for making gestures to the crowd which incited trouble.

[31] After a successful 2014–15, which ended with double conquest, several reports in Italy are keep insisting that Kasami was likely to move to a Serie A club and it is believed that Fiorentina or Inter were the most favourable destination.

On 2 October 2015, media source stated that Olympiacos' former manager Vitor Pereira and midfielder Kasami were prosecuted for provoking episodes in the Greek Cup semi final against AEK Athens.

[36] On 3 August 2016, Kasami became Nottingham Forest's seventh signing of the summer when he joined the reds on a twelve-month loan deal from Olympiacos.

[40] During the 2018–19 season Kasami scored eight goals and made three assists in 20 appearances for Sion and as a result became the subject of transfer interest from Crystal Palace and Turkish club Fenerbahçe as well as fellow Swiss team FC Basel.

[41] On 20 March 2020, FC Sion's president Christian Constantin terminated the contracts of all players without notice after they failed to agree to an 80% salary pay cut during coronavirus pandemic.

Players such as Pajtim Kasami, Johan Djourou and Alex Song among others, wished to secure themselves legally with lawyers before agreeing to sign.

At the beginning of his second season with the club he was also regular starter under new head coach Patrick Rahmen, but then after the winter break and following the change of trainer to Guillermo Abascal, Kasami was used mainly as substitute.

Whilst at Bellinzona, he earned a call-up to the Switzerland U21 team along with teammates Alessandro Ciarrocchi and Frank Feltscher, making his debut against Georgia U21 on 30 May 2010.

He made his debut for the Swiss senior team in a 1–0 win against Slovenia on 15 October 2013 and scored his first goal on 15 November 2013 in a friendly 2–1 defeat against South Korea.