Reeves, 37, the incumbent treasurer, on Tuesday defeated Senate President Pro-Tem Billy Hewes of Gulfport in the Republican primary.
Reeves still has to run in the November general election, but no Democrat qualified for the post. His only opposition in November will be Reform Party candidate Tracella Lou O'Hara Hill of Terry. The incumbent, Phil Bryant, is running for governor.
With 1,748 of 1,873 precincts reporting Tuesday night, Reeves had Hewes 153,649 votes, or 57 percent, to Hewes' 117,805, or 43 percent.
Reeves, a money manager, first ran for public office eight years ago at age 29 when he sought the open office of treasurer against several more-seasoned politicians.
"Elee (his wife) and I are grateful for the warm reception we received all across Mississippi," Reeves said Tuesday night. "People welcomed us into their homes and communities and taught us a lot about Mississippi hospitality. I'm thankful to have the opportunity to serve and will work hard to bring people together to move our state forward."
Reeves pledged to work to bring the Senate together as lieutenant governor.
"I am a conservative guy but we will work across the line to improve the lives of Mississippians," he said.
According to the state Blue Book, Reeves, at 29 in 2003, was the youngest person ever elected to statewide office in Mississippi. He will be one of the youngest to occupy the post of lieutenant governor, which is generally regarded as one of the most powerful postions in state politics. The lieutenant governor presides over the Senate.
Hewes, a 49-year-old insurance agent/real estate broker, had said in recent weeks he had the momentum in the race. But in the end, Reeves' fundraising advantage and name identification advantage was too much to overcome.
Hewes, who has been in the state Senate since 1992 - the last term as pro-tem - had never run a statewide race and struggled to gain name identification outside of his native Gulf Coast region.
Northeast Mississippians, more familiar with Reeves after two previous statewide elections, appeared to favor him. He won Lee County handily and also did well in the heavily populated Jackson suburbs and in fast-growing DeSoto County.
The race, pitting two conservative Republicans, was the most contentious of the primary season. Hewes attacked Reeves for not having any legislative experience and accused him of being beholden to campaign donors who had gotten lucrative work handling the state's bond transactions.
Hewes portrayed himself as a fiscal watchdog and said Hewes, a five-term senator, had overspent and was part of the good-old-boy network in the Legislature.
At one point, Reeves had considered running for governor, but opted to run for lieutenant governor because he said he could influence policy from the post.