When his father played for Detroit, Prince would sometimes come along for batting practice. Contrary to popular belief, Fielder did not hit a home run into the upper deck of Tiger Stadium at the age of 12, but he did hit a home run over the fence as a pre-teen. Fielder set the story straight in a 2007 interview with Fox Sports during a road trip to Detroit.
Since his father took a portion of Prince's signing bonus for negotiating his first contract and gambled it away, the two have not been on full speaking terms.
On the 15th of June that year he collected his first major league hit, a double, off Hideo Nomo, and drove in his first big league run with his second hit of the night at Tampa Bay.
Prince did not get off to a great start in the 2006 regular season, going 0-9 with 7 strikeouts. In his 12th at-bat Fielder finally made a big splash, delivering a game-winning hit that drove home Geoff Jenkins for the winning run in the bottom of the 8th inning against the Pittsburgh Pirates. The hit not only won the game for the Brewers, but secured an opening series sweep. Even with his early season struggles, Prince was named the National League's Rookie of the Month for April, and hit consistently since. On Mother's Day, May 14, 2006, Fielder was one of more than 50 hitters who brandished a pink bat to benefit the Breast Cancer Foundation. With his 18th home run of the year, Fielder broke the Brewers' rookie home run record previously held by Greg Vaughn.
He led all major league rookies with 28 homers in the 2006 season. On defense, he had the lowest zone rating among NL first basemen, .804.
On September 15, 2007, Fielder broke the Brewers franchise record for home runs in a season, hitting his 46th in a game against the Cincinnati Reds. The record was previously jointly held by Richie Sexson (twice) and Gorman Thomas.
On September 25th, Fielder became the youngest player ever to reach 50 home runs in a season, joining his estranged father in the exclusive club. Fielder has stated that he hopes to surpass his father's total of 51 home runs in a season (1990) as a way of exorcising the demons that have come with being the son of a prominent major leaguer. "A lot of people said that's the only reason I got drafted... I don't mind people comparing me to him but I'm a completely different player. One day I want people to mention my name and not have to mention his," Fielder has said. Earlier in the season, Cecil Fielder had told a magazine that it was his famous name that led to his son being such a highly touted prospect. The younger Fielder also saw his contention in the 2007 NL MVP race as a way of proving his father wrong, but gets little else from the rift but motivation saying, "You've got to look at who's saying it. Let's be honest. He's not really the brightest guy."
Fielder ranked first in the National League in home runs (50) in his MVP-caliber 2007 season, was 2nd in slugging percentage to teammate Ryan Braun (.618), 2nd in at bats per home run (11.5) and OPS (1.013), 3rd in RBIs (119) and extra base hits (87), 4th in total bases (354) and hit by pitch (14), 5th in intentional walks (21) and sacrifice flies (8), 7th in runs (109) and times on base (269), and 9th in walks (90).
In 2007 he led all major league first basemen in errors, with 14, and was last among eligible major league first basemen in range factor (8.49).
On June 19, Fielder hit the second inside-the-park home run of his career, against the Toronto Blue Jays.
On Aug. 4, Fielder and teammate Manny Parra got into a scuffle in the dugout during a game against the Cincinnati Reds in which Parra was the starting pitcher. They were having a brief conversation, which led to Parra throwing his jacket down and Fielder shoving him. Fielder had to be restrained by teammates Ray Durham, Dave Bush, J. J. Hardy, Ryan Braun, and pitching coach Mike Maddux. ESPN Television reported that night that the dispute was over Parra heading back to the clubhouse after being pulled from the game instead of staying in the dugout to watch the Brewers bat in the next inning. Baseball Tonight also reports the exchange was started when Parra told Fielder to "get off his fat ass and play defense." Manager Ned Yost said reporters asking questions about the incident was as rude as "going over to the neighbors' house after they've been fighting and asking about it."
On Sept. 23, Fielder hit his 2nd walk off home run against the Pittsburgh Pirates, helping the Brewers keep pace with the New York Mets in the NL Wild Card race.
Fielder was named the National League Player of the Week for the week of September 15-21 after he batted .462, with 27 total bases, six doubles, 11 RBI, .533 on-base percentage, and a 1.038 slugging percentage.
Fielder ended the 2008 regular season with a .276 batting average, 34 home runs, 102 RBI, 86 runs and 84 walks. The Brewers finished 90-72, earning the NL Wild Card and making the playoffs for the first time since 1982. They faced the Philadelphia Phillies and were eliminated in 4 games.