Kadmon makes Rezurock, a treatment for patients as young as 12 who suffer from chronic graft-versus-host disease, a complication that can occur after a bone marrow or stem cell transplant.
"The acquisition supports Sanofi's strategy to continue to grow its General Medicines core assets and will immediately add Rezurock (belumosudil) to its transplant portfolio," the French firm said in a statement.
Rezurock is a "real gem" that adds to Sanofi's transplant medicine portfolio, said executive vice president for general medicines, Olivier Charmeil.
Kadmon is also testing the drug to treat diffuse cutaneous systemic sclerosis, a rare disease that affects the skin and internal organs.
Kadmon shareholders will receive $9.50 per share in cash in the deal, which was unanimously approved by the boards of both companies. Shares in Kadmon had closed at $5.23 in Tuesday trading.
The acquisition is expected to be completed in the fourth quarter.