AIG Europe won a second three-year contract to be sole supplier for Boots travel insurance products.
The company was reappointed after a competitive tender.
It will underwrite all Boots' travel policies, which cover city breaks, single trips, multi-trips and gap years.
Boots even sold travel insurance on Christmas Day when many other outlets were closed.
Boots Insurance sales and marketing manager Mike Flint said more than half the policies sold on Christmas Day were bought from the chain's airport stores, which are among the 620 outlets that sell insurance.
Policies are also sold over the internet and by phone.
Flint said pre-sale health screening helped ensure customers were suitable for the cover.
AIG Europe travel manager Richard Bodin said: "We are delighted to continue our relationship with Boots and will ensure that we exceed their expectations in supporting their competitive edge in the travel insurance sector."
Boots also sells cover for dentistry, spectacles, extended warranties for photographic equipment sold in its stores and healthcare cash plans.
Its dental insurance is underwritten by Munich Re, its healthcare cash plans are underwritten by Westfield and the other areas are underwritten by AIG Europe.