He has already served in a very high leadership role in the Mormon Church. I don’t know if he still holds the position or if it compares with the power of a Cardinal in the Roman Church.
Yes Bishop Romney was a Bishop, and then a Stake President, over other Bishops.
Romney is expected to become the Mormon version of a Cardinal, and could possibly go all the way to Pope/Prophet, his uncle was in line for that Holy position when he died.
Mitt is thought by many Mormons to be fulfilling the "White Horse Prophecy" if he becomes President of the United States.
Temple Mormon, Harry Reid already runs the Senate.