[4] In 1992, he was expelled from the Palestinian territories by Israel to southern Lebanon and upon his return in 1995, Seyam was arrested by the Preventive Security Service (PSS) dominated by Fatah.
[3][4] Seyam was reported by Hamas as one of the pioneer of mortar and Qassam rocket attacks on Jewish settlements in the Gaza Strip, which caused them to be virtually besieged from 2001 to their evacuation by Israel in September 2005.
[citation needed] Seyam became one of the members of the Hamas "collective leadership" in Gaza after the 2004 killings of founders Ahmed Yassin and Abdel Aziz al-Rantisi.
[3] Seyam was close to Yassin and Hamas secretary-general Khaled Mashal, that latter whom he accompanied on a diplomatic visit to Moscow, Russia.
[4] He represented the Gaza electoral district of the Palestinian Legislative Council as a Hamas member after being elected with the most votes for any single candidate.