The 25-year-old has signed a five-year contract with the option to extend it for a further year.
Haller’s £45m transfer fee eclipses the £41m the Hammers paid Lazio last summer for Brazilian midfielder Felipe Anderson.
Haller becomes West Ham’s fourth summer signing after the captures of Spanish midfielder Pablo Fornals and goalkeepers Roberto and David Martin.
West Ham United turned their attention to Haller after missing out on Uruguay forward Maxi Gomes, who moved to Valencia from Celta Vigo.
Haller will reinforce a West Ham forward line that has recently seen the departures of Marko Arnautovic, Andy Carroll and Lucas Perez.
"It means a lot [to be the record signing]," Haller said in a statement.
"It proves that the club [has] really wanted me for a long time.
"I felt this desire to sign me and I’m really happy to sign, also. it is an ambitious club, a nice club, a nice city and nice fans too.
"For me I can guarantee that I will give 100 per cent for the club because the club has given me this confidence and I will try to give it back every day in every game.
"I will always give 100 per cent and respect the club. I think this is a normal thing and that I can guarantee. I know it’s a big transfer and there is a lot of expectation around me, and I just want to make people proud of this transfer and I will give everything I have."
Haller, who scored 15 goals in 29 Bundesliga matches for Frankfurt last season, is the second high-profile forward to leave the German side in the off-season after Real Madrid priced Luka Jovic away from the club.
