Irvin will become the 11th Giants player to have his number retired and will be joined by Mays, Willie McCovey, Juan Marichal, Gaylord Perry and Orlando Cepeda for pregame ceremonies.
"It is quite an honor," Irvin said Wednesday in a phone interview. "I wasn't able to play with the Giants in San Francisco, but being able to play with Mays was special. And I was out there when they celebrated the 1954 World Series [in 2004] and that was special. It was a magnificent gesture."
The 91-year-old from Haleburg, Ala., played in the Negro Leagues with the Newark Eagles from 1937-42 and 1946-48 and was a five-time All-Star.
Giants infielder Emmanuel Burriss, currently on the disabled list rehabbing a broken left foot, said retiring Irvin's No. 20 will further cement the Hall of Famer's legacy.
"Just having that honor is something that really establishes how people look at you," said Burriss, the only black player currently with the Giants. "For that to happen, it's just one of those things that should be noticed throughout the league as much as the city. It means a lot, it definitely means a lot."
Outfielder John Bowker currently wears No. 20 for the Giants. Bowker learned of Irvin's honor about a half-hour before the Giants took batting practice Wednesday.
"I just found out he was the first black player with the Giants, so obviously it's something that's pretty special," Bowker said. "It's a good reason they're retiring it."
Bowker said the club will allow him to continue wearing No. 20 for the remainder of the season. He wore No. 21 last season but gave it up to trade acquisition Freddy Sanchez last season. Bowker said he isn't sure which number he'll wear next season, adding he's not superstitious when it comes to jersey numbers.
After his playing career, Irvin served as a scout for the Mets and a public relations specialist for the Commissioner's Office and was inducted into the National Baseball Hall of Fame in 1973.
He accumulated a .293 batting average, 97 doubles, 31 triples, 99 home runs and 443 RBIs during his eight-year Major League playing career.
The June 26 ceremonies are scheduled to begin at 3:30 p.m. PT.