He said: "There are many crossovers between the structure, the service delivery and the ethos of the two charities."
Rudd, who will start in March, succeeds David King, who is leaving to lead children's hospice charity Chase (Third Sector, 27 September 2006).
He began his career in the voluntary sector in 1999, when he joined the RSPCA as regional manager for Wales. He is a former Royal Marines officer and has worked in business.
Steve Evans, chair of Samaritans' trustees, said: "Dominic's consultative style and enthusiasm for working with volunteers combine with a strong leadership style to make him an outstanding candidate."