A native of Jersey City, New Jersey, Geraghty was a graduate of Villanova University, where he received a degree in journalism. He went right from the Villanova campus to the 1936 Brooklyn Dodgers, but would appear in only 70 Major League games, 51 with the Dodgers in his rookie season and 19 more with the Boston Braves (1943–44). He compiled a batting average of .199 in 146 at bats, with his 29 hits including four doubles. He also played ten seasons in the minor leagues. Geraghty threw and batted right-handed, stood 5 feet 11 inches (1.80 m) tall and weighed 175 pounds (79 kg).
On June 24, 1946, Geraghty survived one of the greatest tragedies in baseball history, when the bus carrying his minor league team, the Spokane Indians of the Class B Western International League, crashed while attempting to avert an oncoming car on a rain-slicked mountain pass. Nine players were killed; Geraghty was among the injured. He sustained a severe head wound when he was thrown through a window before the bus burst into flames, but was able to climb up the hillside and signal for help. The Spokane club was decimated and could only continue the season with players loaned from other teams and organizations. "I guess I'm pretty lucky", Geraghty told the Associated Press the day after the crash. "I was thrown right out a window. I took the window frame right with me. I remember flying out the window, but I must have been knocked out because I don't remember landing."
Despite his head injury, Geraghty was named the immediate replacement for Mel Cole—the team's catcher and player-manager who perished in the crash—as the Indians' first post-accident skipper. But his injuries were too serious and former big-leaguer Glenn Wright assumed the reins for the rest of 1946. Geraghty was able to return to Spokane to manage the Indians in 1947, and he led them to a second-place finish and 87 victories. His health, however, would never be the same. He would manage in the minors for the next 16 seasons, but he was troubled by heart disease, cardiovascular disease and ulcers, and developed a reputation as a heavy drinker.
In his 17-year managing career, Geraghty won 1,317 games and lost 1,021 (.563) and won five pennants in seven years (1953–59) while piloting Class A Sally League and Triple-A American Association farm clubs of the Braves, then based in Milwaukee. In the ten seasons of 1953 through 1962, a Geraghty-managed team never finished lower than second place. But his impact was felt beyond mere wins and losses. In 1953, Geraghty managed a racially integrated team in the Jim Crow South with the Jacksonville Braves, and one of his players was 19-year-old Henry Aaron.
Aaron, wrote author and former minor league pitcher Pat Jordan in his 1975 memoir A False Spring, "believed that Ben Geraghty was the greatest manager who ever lived, certainly the greatest manager he ever played for ..." In addition to his on-field strategic acumen and his ability to develop playing talent, Geraghty, a white man, regularly confronted the rigid racial segregation of the times, insisting that he and his African-American players be served as equals at the finest restaurants. "Invariably, they would be refused service", Jordan wrote. "While Aaron waited nervously outside, Geraghty complained loudly to the management ... They [would go] to the next best restaurant, and the next and the next, until Geraghty finally located one that would serve [them]."
But Geraghty would never be called to manage or coach in the Major Leagues. He was strongly considered for the Braves' managerial opening when Fred Haney stepped down following the 1959 season, but Chuck Dressen was hired instead.
Ulcers then sidelined Geraghty for much of the 1960 season, while he was in the midst of a three-year term as skipper of Milwaukee's Louisville Colonels Triple-A farm club. In 1962, he left the Braves and joined the Cleveland Indians' farm system as manager of their new Triple-A International League affiliate, the Jacksonville Suns. That January he also underwent a four-hour operation in a Jacksonville hospital to correct a circulatory condition. Recovering in time for spring training, he led his 1962 Suns to 94 victories and earned his second Minor League Manager of the Year Award and final pennant. The following June 18, in Jacksonville, in the middle of his second season in the Suns' job, Geraghty was stricken with a fatal heart attack, one month shy of his 51st birthday. He is interred in Evergreen Cemetery, Jacksonville.
"I don't know of another manager in baseball whom the paying fans held in so much respect", The Florida Times-Union's sports editor wrote upon Geraghty's death.
Before his 1946 injury from the Spokane bus accident, Geraghty also was a basketball coach, serving as an assistant with the varsity at Seton Hall University.