A five-year deal for an undisclosed fee has been signed by Mikkel Damsgard.
In 49 appearances, Damsgaard scored two times.
He scored a free-kick against England in the Euro 2020 semi-final, before the Danes lost in extra time.
Damsgaard joins Brentford for an undisclosed fee which is reported to be around 15m euros (£12.7m).
The player will be training this week before the game against Manchester United on Saturday.
The Bees came back from 2-0 down to tie the game.
The addition of Damsgaard is the fifth summer signing for the club.
He scored four goals in 16 appearances for his country and 11 appearances for Sampdoria last season.
After making his debut at 17 years old, Damsgaard spent three seasons at the club before moving to Sampdoria.