Al-Khatib began playing football at Al-Karamah SC, he was included in the club's categories U-14, with whom he played for two seasons. One of the most important achievements of Al Khatib with youth Al Karamah was the victory of the Republic Cup and the title of the league's top scorer twice 1994–95, 1995–96. He then went on to play for Al Karamah U-17 in 1997, where he was crowned with the league title in the same year.
He also won the top scorer title. All this helped the young boy reach the youth team. During two seasons with U-19 team, he managed to win the league title and the second scorer.[3]
Al Karamah
Al Khatib started his professional career in the Syrian Premier League with Al-Karamah in the Season 1999–2000. On 6 October 2000, he scored his first goal in the Syrian Premier League against Al-Futowa which 1–1 finished.
During 2001, he spent two trials in Belgium; first with Gent and the second with Anderlecht.
Al Naser
In August 2002, he transferred to Kuwaiti Club Al-Naser, and played in Kuwaiti Premier League for the first time. He then moved to Al-Arabi, which also competed in the Kuwaiti Premier League.
In June 2005, he was loaned out to Al-Ahli in Qatar for one match, and played alongside Pep Guardiola.
Qadsia
On 24 August 2009, Al Khatib signed a two-year contract with Al-Qadsia in the Kuwaiti Premier League and played alongside his old teammate Jehad Al-Hussain.[4]
In July 2012, he participated in three games with Nottingham Forest, scoring once in a trial of month.[5] He impressed manager Sean O'Driscoll enough that the club were looking to sign him on a permanent basis but he was denied a work permit and the club was unable to sign him.[6]
He became a free agent at the end of the 2013–14 football season and returned to Kuwait. He declined an offer from Kuwait SC and joined Al-Arabi SC on a 2-year deal.
During the first derby against Al-Salmiya, Al-Khatib scored his 100th league goal, but Al-Arabi SC lost the match 3–2.[7]
Al-Khatib ended the season with 20 goals and shared the VIVA Premier League 2014–15 top league scorer with Patrick Fabiano. His total goal tally in all competitions was 24 goals. In 2015–16, he was selected in the VIVS Premier League 1st Team alongside teammate Ali Maqseed. Al-Khatib also won the VPL Golden Boot and top scorer of Al-Arabi with 27 goals; his highest tally in any season with any team.
Al Salmiya
In September 2017, he joined to Al-Salmiya, and scored 11 goals in his Kuwaiti Premier League.
He became the best goalscorer in Kuwait Premier League history after he scored 147 goals, exceeding many Kuwaiti legends.[8]
Retirement
On 29 September 2019, Al-Khatib announced his retirement from football after spending the whole summer without a club.[9] He finished his career scoring 349 goals[a] to achieve the 19th place in the list of world's best goal scorer of 21st century,[10][11] as well as being the all-time top scorer of all Kuwaiti domestic competitions with 210 goals.[12] He was also the all-time top scorer in the Kuwaiti Premier League, with 162 goals, before Bader Al-Mutawa broke his record in 2024.
From 2012 to 2017, Al-Khatib boycotted the Syrian national football team to protest president Bashar al-Assad and his government's airstrikes against Al-Khatib's hometown of Homs. On 23 March 2017, al-Khatib re-joined Syrian national football team and expressed support for Assad.[14]
He was not included in the final squad of 2019 AFC Asian Cup after getting injured about a month before the tournament, although, he claimed that he was capable of participating if the manager called him because his injury was minor and he could be part of the second match at least. It was really disappointing to him as he mentioned many times on Bein Sports as he was one of the pundits there during the tournament.[15] He was one of the first people who asked to sack Stange after the lost against Jordan.[16] In an interview diffused 20 March 2019, he denied any rows between players about the captaincy before and during Asian cup 2019, and denied also what Omar Al Somah said earlier about falling out for the captaincy armband.[17]
In 2019–20, Al Khatib became an assistant coach at Al-Salmiya.[19] In June 2021, he was appointed as the head coach of his hometown club Al Karamah.[20] A few days later, Al-Khatib refrained for Al Karama coaching due to "family circumstances". Subsequently, he was appointed as an assistant coach at Al-Naser.[21]
In April 2022, Firas became the coach of the Iraqi club Zakho.[22] Three months later, in July 2022, Firas returns to Kuwait as coach of Al-Fahaheel.[23] In May 2024, he extended his contract with the latter until 2025.[24]