The building was originally used as a game larder and then a summer house, before being converted into a butterfly house in 1946 based on plans by butterfly expert L Hugh Newman.
The garden team refurbished the butterfly house based on articles written by Newman and held consultations with Defra and Butterfly Conservation before restocking with larvae from locally occurring species.
National Trust nature conservation adviser Matthew Oates said: "Chartwell was way ahead of its time with its focus on making sure that they had a wildlife-friendly garden and it was also a pioneer of butterfly gardening.
"Mixed in with the more formal nature of an English country garden, Churchill insisted that Buddleja and thistles were planted to attract butterflies and insects."
Butterfly Conservation chief executive Dr Martin Warren added: "Many UK butterflies are in dramatic decline and so it is great news that they are thriving at Chartwell this year."
Visitors to Chartwell will be able to view the butterfly house and stroll along the butterfly walk.