The rugby league side share the KC stadium with the football club where Pearson is now head of football operations.
Pearson has purchased the entire shareholding at the outfit, which he previously tried to take over in 2002.
"I have now purchased the entire shareholding of Hull FC and will be investing further funds into the club to ensure it can now kick on a develop into one of the very strongest Super League clubs," he said.
"I have not invested significant sums into the purchase of Hull FC to see the club stand still," he added.
Pearson has previously had spells as commercial director of Leeds United and chairman of Derby County.