Born to Grady and Donna Sizemore, Grady Sizemore III was born on August 2, 1982 in Seattle, Washington. Grady attended Cascade High School in Everett, Washington where he was a three-sport-star. Grady set a Cascade record with 3,081 rushing yards and 16 interceptions. During his senior season at Cascade, Grady hit .457 with 10 doubles, 7 Home Runs, 24 stolen bases, and 20 runs batted in. Along with his many accalades on the field, Grady boasted a 3.85 GPA which made him a highly-touted student athlete. Grady was a heralded recruit to play both football and baseball for The University of Washington. He was also heavily recruited by Arizona State, Washington State, Clemson, and California.

All of the college recruiting ended when the Montreal Expos selected Grady in the third round of the 2000 Draft. Grady signed his contract on June 16 which included a 2 million dollar signing bonus. Grady played his first pro-ball season for the Gulf Coast Expos where he ranked fifth in both games played with 55, and in at-bats with 205. Grady spent his 2001 season playing for Clinton of the Midwest League. There he stole 32 bases and finished second in the league with 81 walks.

Grady started his 2002 season with Brevard City and then halfway through the season the Montreal Expos dealt Grady Sizemore, Brandon Phillips, Cliff Lee, and Lee Stevens to the Cleveland Indians for Bartolo Colon and Tim Drew. Grady started his tenure with the Cleveland Indians organization playing with single A Kinston. Grady was then named to the Sportsticker All-Teen Team after hitting .343 (59-172) with 9 doubles, 3 triples, 3 Home Runs and 20 RBI in 47 games with Kinston.

2003 proved to be a very big year for young Grady. In just his first full season with the Cleveland Indians organization, Grady won the Lou Boudreau Award as the organizations top position player. Grady led the organization in runs (96) and hits (151), finished third in average (.304) and tied for third in RBI (78) among Indian farm system players. Grady finished the season tied for the Eastern League lead in triples with 11 and tied for second in runs with his 96.

Grady was named to the 2003 Eastern League Rookie of the Year and was the runner-up for the Eastern League MVP Award. Grady also won the Larry Doby Award which goes to the Most Valuable Player in the Futures Game. Grady went 2-3 with a homerun and 2 RBIs in the US Win. The honors just kept rolling in when Grady was named to the 2004 Olympic Team after a dazzling performance in the Arizona Fall League during the try-out proportions. Grady entered the 2003 season as the Indian's seventh best prospect. After the 2003 season he entered the 2004 campaign as the Indian's top prospect in the entire organization.

2004 marked the year that Grady would make his major league debut. On July 24th, Grady entered the game as a defensive replacement against the Chicago White Sox. Grady's first major league start came the next night and his first major league hit came on the 23rd off of Kansas City pitcher Mike Wood. Grady was sent back down to AAA Buffalo where he started the season to get more at-bats. There he helped lead the Bisons to the International League Championship.

Grady won a roster spot the next season when Juan Gonzalez went down in Spring Training with a hamstring injury. Grady never handed back over his spot and went on to post a .289 average, 22 Home Runs, 81 RBI, and 22 stolen bases in 2004.

During the offseason Grady resides in Mill Creek, Washington and Tempe, Arizona.