Finland used a variety of FN pistols prior to WW2, and had already evaluated the High Power when Russian invaded and the Winter War began. With an urgent need for more arms, Finland ordered a batch of High Power pistols, which FN was happy to include with the other arms orders already being delivered to Finland. In total, the Finns bought 2,400 of them, with 900 delivered in February 1940 and 1,500 in March 1940. All of them were bought as rigs with leather holsters riveted to flat board shoulder stocks (note that a Finnish pistol with a Finnish-contract original stock is exempted form the NFA in the US, and need not be registered as a short-barreled rifle).
This delivery schedule meant that only a few were available in time to be used in the Winter War, and they saw much greater use in the Continuation War. They were particularly appreciated by the Finnish Air Force as pistol survival weapons. This is often misinterpreted to mean that they were exclusively used by the Air Force; in fact the quantity of Finnish aircraft was small enough that only a small fraction of the pistols were issued to pilots.
Finnish contract pistols have serial numbers falling between 11,000 and 15,000 (and not all guns in that range are Finnish). The stocks were marked in large numbers with the serial number of the gun, although matching rigs are quite scarce today. Some, but not all, were later marked “SA” by the Finnish Army. During the continuation War some of the holsters were separated form the stocks, and some of the pistols had new square front sights put on (a common Finnish preference, done to Lugers as well).
About 40% of the High Powers were lost or rendered unserviceable by the end of the Continuation War. The remainder were kept in service until the 1980s, when they were replaced by the Browning Double Action and slowly sold as surplus.