He is very available as free agent after he left Ajax and now set for Premier League return.
The 35-year-old will join the Bees on a two-year deal after the Dutch club agreed to end his contract a year early.
Henderson had considerable interest from top clubs in England and Europe but Brentford have won the race to sign the former Liverpool skipper.
Playing in the Premier League will provide Henderson with the platform to stay in Thomas Tuchel's England squad before next summer's World Cup.
Henderson left the Reds to join Al-Ettifaq but his time in the Saudi Pro League lasted less than six months before he joined Ajax in January 2024.
He made more than 50 appearances for Ajax but exited the club having narrowly missed out on the league title, with PSV Eindhoven crowned champions on the final day of last season.
Henderson was left out of Gareth Southgate's Euro 2024 squad, as he had not played for England since 2023.
After Tuchel's appointment as England head coach in January, Henderson has featured in both of the German's squads, making three appearances.