Born in Haifa, Sandberg studied law at Tel Aviv University, gaining an LLB. He joined the Tzomet party, and became a member of its secretariat in 1988. He also served as the party's legal adviser and chairman of its Haifa branch. In 1992 he was elected to the Knesset on Tzomet's list. He was re-elected in 1996 and in November 1998 was appointed Deputy Minister of Education. On 23 February 1999 he left Tzomet to become a founding member of the Israel in the Centre party (later renamed the Centre Party), but on 22 March he left the new party to establish his own faction, HaTzeirim. On 29 March merged HaTzeirim into Shinui.
In January 2006 Sandberg was amongst the Shinui MKs which left the party to establish the Secular Faction. On 5 February he and Hemi Doron left the new faction to establish the National Home. Prior to the 2006 elections the two joined Likud, but were not included on its list, and thus lost their seats in the election.
Sandberg is expected to be named Cabinet Secretary by Prime Minister Designate Benjamin Netanyahu should he be able to form a government.