The 63-year-old Dutchman is currently attempting to revitalise United after replacing David Moyes at Old Trafford in the summer.
Writing in his updated autobiography, Ferguson described Van Gaal as "a good choice".
He said: "Louis, who took the job, is what I would call a managers' coach
He's one of these committed ultra-professionals
Football is his life.
"Wherever he has managed, every footballer will have learned from him
He's strong, single-minded, as he showed again with the Netherlands at the World Cup - a marvellously entertaining tournament which supported my earlier point about teams counter-attacking nowadays en masse.
"I like Louis and have always had a good rapport with him
If I had to choose one word for him it would be 'formidable'.
"His urge is to play attractive football
He likes to watch players play and players train and to be involved at all levels, including in the development of young players.
"His background at Ajax shows that his faith in youth will not diminish
He was a good choice."
Ferguson also applauded Van Gaal's decision to appoint former midfielder Ryan Giggs, who took over from Moyes on a caretaker basis, as his assistant
Predicting that the Welshman would thrive under the older man's influence, he said: "Louis could help Giggs learn about this business
In turn, Ryan could help Louis in understanding the inner workings of United.
"As I look back on all those trophies, and those 963 appearances and 168 goals, I recall him as a physical freak
How he could have performed at the level he played at for all those years is beyond me.
"With Giggs I found perfection."
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Source: PA