The 21-year-old Canadian striker, who has joined the Perth club on a season-long loan deal from West Brom, moved to the Hawthorns in January but was loaned back to former club Vancouver Whitecaps in April.
"I first heard of the club's interest a few weeks ago. They had sent scouts to watch me when playing for Vancouver Whitecaps. I've been playing solidly for the last 18 months because West Brom loaned me to Vancouver back in April so I'm match fit," Haber told Saints' official website.
The Vancouver-born striker, who also holds an Austrian passport, continued: "I've heard the SPL is up-tempo and physical so it will be like the Championship in England.
"This is the real deal for me."
St Johnstone boss Derek McInnes, a former West Brom skipper, said: "West Brom have high hopes for him but having stepped up a level into the Premiership they wanted him to go out on loan rather than be kicking his heels at The Hawthorns.
"He is young, hungry, has real pace and he's keen to learn."
Source: PA
Source: PA