In February 1943, Yeo-Thomas was parachuted into Normandy. From here, he travelled to Paris where he had been given the task of organising the various resistance movements that were found throughout France. In April 1943, he returned to France where he was given the vital task of trying to work out why so many members of the French Resistance were being arrested in Paris. His influence and guidance ensured that the various resistance movements used much greater security not only within each unit but between the various factions.
On one of his inspections of the resistance, Yeo-Thomas was appalled at how badly they were equipped with weapons. In an interview with Winston Churchill, he claimed that the resistance would only operate better, if they had access to better armaments. In February 1944, Yeo-Thomas was parachuted back into France to assess the damage done by the arrest of two leading resistance leaders. During this work, he was captured and tortured by the Gestapo. Yeo-Thomas was sent to Buchenwald concentration camp where, in November 1944, he escaped. By the spring of 1945, Yeo-Thomas had reached the safety of the advancing Allies in France.