Norby got 62 percent of the vote. Democrat John MacMurray came in second with 32 percent, followed by Green Party candidate Jane Rands with 6 percent.
The runoff election was held because no candidate received 50 percent of the vote needed to win in last November's special election.
The 72nd district includes Fullerton, Anaheim, Placentia, Orange, Brea, Yorba Linda and La Habra.
Former Assemblyman Mike Duvall stepped down from the office in September after he was videotaped at a committee meeting telling a colleague about his affair with a lobbyist.