Sampson, who succeeds Chris Holmes, moves from his current post as chief executive of the Rehabilitation for Addicted Prisoners Trust.
The majority of his career has been in campaigning and policy work aimed at reforming the criminal justice system. He spent five years as deputy director of the Prison Reform Trust and three years setting up the prisons ombudsman.
Sampson said there is now "a real opportunity to secure lasting change for homeless people" and promises to adopt "holistic solutions" to making it happen.
He said: "Homelessness and bad housing act as a catalyst for other problems, helping to pitch people into a cycle of poverty and social exclusion."
Robert Silverman will continue to work as acting director until January.