The deal with Freeman is worth between $125 million and $135 million, according to media reports. Financial terms were not released.
It is the longest contract in Braves history, supplanting the six-year, $90 million contract given to Chipper Jones in 2000, according to MLB.com.
It comes the same day Atlanta reached a two-year, $13.3 million deal with right fielder Jason Heyward, also 24.
Both players are represented by Excel Sports Management and were eligible for salary arbitration.
General manager Frank Wren said reaching a deal with each player was not a sign of the team giving up on its "file and trial" strategy of ending negotiations with players after the arbitration deadline for exchanging salary figures had ended. That date was Jan. 17.
"It's a very strict policy," Wren said, according to the Atlanta Journal-Constitution. "Unless talks are about a multiyear contract extension, that's always been the policy."
Freeman broke into the major leagues in 2010 and has improved in every year since. He is coming off a 2013 campaign in which he hit .319 with 23 home runs, 109 RBIs and 89 runs scored in 147 games, making the National League All-Star team for the first time.
"Freddie has established himself as one of the best young talents in the game," Wren said in a statement released by the team. "We are excited to sign one of our own homegrown players to a contract that will keep him in a Braves uniform for the next eight seasons."
Freeman's wins above replacement was 5.4, which ranked fourth in the majors among first basemen.
Also, Freeman became the first first baseman since Hall of Famer Orlando Cepeda to post three 20-home run seasons through his age-23 season, according to ESPN Stats & Information. His three such seasons are tied for the most in major league history among primary first basemen.
Freeman was in the news last week, too. Former teammate Jones rescued him on a four-wheeler after he was stranded on the highway for five-plus hours during a deep freeze that had engulfed much of the Southeast.
Jones saluted Freeman's new deal on Twitter on Tuesday:
Oh my! @FreddieFreeman5 got broke off! Can ur new chauffeur get a lil bit? Jk bruh, u deserve it! Dinner tmrw night. Ur treat???The deals with Freeman and Heyward leave All-Star closer Craig Kimbrel as the lone Braves player left in arbitration.
- Chipper Jones (@RealCJ10) February 4, 2014
Heyward said he was happy to avoid arbitration.
"In my head it basically says to me, let's go play some baseball," he said.
Information from The Associated Press was used in this report.