Between 1922 and 1925, Dicker represented Geneva in the National Council.
He returned to the National Council in 1928, and would remain a member of that body until 1941.
Dicker defended Nicole in a legal case in May 1933.Being a prominent Jewish political leader, Dicker was subjected to violent antisemitic attacks.
On November 9, 1932 the far-right National Union convened a meeting in the municipal hall in Plainpalais, a meeting intended to function as a tribunal against Nicole and Dicker.
A leftist countermanifestation was organized.
Violence broke out between demonstrators and army, killing 13 people and injuring 65.Dicker was one of four Socialist parliamentarians that sided with the Swiss Socialist Federation when the Socialist Party went through a split in 1939.
The Swiss Socialist Federation was banned on May 27, 1941 and Dicker and the other parliamentarians of the party were expelled from the National Council on June 11–12, 1941.