I know a friend who has been illegal in us for 9 years. He is marrying an american woman now in order to become legal, get the work permit and become ultimately a us citizen.

Is all this possible for him to become legal? If yes what would be the procedure after getting married to american woman.

First, he must have a bona fide marriage, to have a shared life together and not just for an immigration benefit.

For him to get permanent residence this way, he must be eligible for AOS in the US, this will depend on "how" he is illegally here in the US.

Generally, if he entered the US on his own visa and passport and overstayed, the marriage to the USC will forgive the overstay of the I-94 and any unauthorized employment under INA section 245(a). If he is here based on a misrepresentation, generally, he will need to qualify for a waiver under section 212, based on a hardship to the USC spouse.

Please also note that he must not be inadmissable for criminal or security grounds, among others.

Consult with an experienced immigration attorney or a certified specialist. If this was helpful, rate this answer! Good luck to your friend.