Deal, a former nine-term congressman from Gainesville, soundly defeated former Democratic Gov. Roy Barnes, who was running to get his old job back after being ousted in 2002.
With 99 percent of precincts reporting, unofficial returns showed Deal with 53 percent of the vote to Barnes' 43 percent. Libertarian John Monds pulled 4 percent of the vote.
"Tomorrow the work starts all over again," Deal told cheering supporters in an Atlanta hotel ballroom. "Up and down the ballot, Georgia has placed its faith in the Republican Party and we're not going to let them down."
The GOP claimed seats from lieutenant governor to attorney general to agriculture commissioner. And they picked up two Georgia congressional seats held by Democrats.
The win cemented Republican control in a state that not too long ago was ruled by Democrats.
Deal beat back questions throughout the campaign about his ethics and personal finances.
Barnes - who attacked Deal relentlessly throughout the campaign for using his congressional office for personal gain - said late Tuesday night he had wished his opponent the best in a concession call.
"I am reminded of the words of the apostle Paul, one my favorite quotations. 'I have fought the good fight, I have run the good race, I have finished the course, I have kept the faith,'" Barnes said in a brief speech.
Deal, who will replace term-limited Republican Gov. Sonny Perdue, was buoyed by a strong anti-Washington tide that energized GOP voters upset with President Barack Obama and Democrats in Washington.
He ran a race in which he pledged to stick to his conservative credentials and keep taxes low. Barnes vowed to end teacher furloughs and reduce the state's high unemployment rate.
During the campaign, Deal fought off questions about his ethics and his personal finances in a race that featured dueling attack ads and big ad buys by outside interest groups.
Barnes was on the defensive about his ties to Obama and worked to demonstrate his independence from Washington. Barnes pledged his support for an Arizona-style immigration law the Obama administration is challenging in court and also criticized portions of the president's health care overhaul.
In one ad by the Republican Governors Association, images of Barnes and Obama were overlaid under the title "Roybama." Deal's consistent message was that Barnes did not deserve a second chance leading the state.
Needing to gain ground in a state that has voted reliably Republican in recent years, Barnes wasted no time attacking his GOP rival. He labeled Deal corrupt and suggested he has used his congressional office for personal gain.
The Barnes campaign frequently cited a congressional ethics report released earlier this year that said Deal may have violated rules that govern the conduct of House members. Deal stepped down from Congress in March to concentrate on the governor's race, effectively ending the congressional investigation.
Deal denied any wrongdoing, but Barnes assailed Deal's ethics in debates and on the airwaves. Barnes also raised questions about Deal's fitness to oversee the state's finances after it was reported that Deal was so deeply in debt that he'd put his house on the market.
Deal and his wife, Sandra, were left on the hook for a $2.3 million loan after his daughter and son-in-law's sporting goods store failed. Deal has said he will make good on the debt and has already liquidated about $750,000 in retirement funds to pay it down.
During one debate, Barnes asked voters who they would want to run the state's finances.
The strategy turned off at least one voter, Chris Simon, who manages a family owned hotel on Tybee Island.
Simon said he was outraged that Barnes made an issue of the loan and voted for Deal.
"I've helped my children, too, and I didn't think he should have brought that up," said Simon, 63, who considers himself a Republican. "I wouldn't have voted for Roy Barnes if he was the only one running because of that."
An early part of Barnes' campaign centered on making amends for putting off voters, particularly teachers, during his first term. This year he received the backing of the Georgia Association of Educators, which withheld their endorsement in 2002.
Atlanta resident Ronny Gutfreund, 32, said he cast his vote for Barnes.
"I just like what his stance on most issues were," said Gutfreund, a radio promoter. "Most of the issues that I researched, he was in line with me on."
In the campaign's homestretch, Barnes sought to rally women voters, rolling out a tough attack ad that suggested Deal tried to weaken the state's rape shield law when he was in the state Senate in the 1980s and voted against toughening domestic violence laws.
Deal disputed Barnes' claims and said the attack on decades-old votes suggested Barnes was desperate for an edge.