Randle attended Fork Union Military Academy during his elementary and high school years. He focused on track and field, competing in different events and clocking 9.6 seconds in the 100-yard dash at one point. He also practiced basketball.
He didn't play football until his senior year, because his athletic director Gus Lacy (who also served as his guardian) feared he would get hurt. Unfortunately he broke his collar in his third game.
The Virginia Military Institute offered him a scholarship, but he couldn't adapt and returned home before the end of his first year. He decided to walk-on to the University of Virginia and eventually earned a football scholarship
In his first two seasons he didn't have a big impact, because he played as a wingback in the team's run-oriented offense. In 1958, the offense changed into more of an open passing attack, and he finished second in the NCAA with 47 receptions and first in kickoff returns. In college, he also practiced basketball (one season) and track(four seasons), where he set a record by running the 100-yard dash in 9.6 seconds. He also ran the 220-yard dash in 20.7 seconds.
In 1991, he was inducted into the Virginia Sports Hall of Fame.
Randle was selected by the Chicago Cardinals in the 19th round (218th overall) of the 1958 NFL Draft, with a future draft pick, which allowed the team to draft him before his college eligibility was over.
In 1959, although he was one of the fastest players in the league as a rookie, he had trouble adapting to the professional game, registering only 15 receptions, but veteran defensive backs Dick 'Night Train' Lane and Jimmy Hill taught him how to get open.
In only his second season in the NFL, Randle had a break-out year registering 62 receptions (second on the league) for 893 yards and 15 touchdowns (led the league) and was named first-team All-Pro by the Associated Press (AP), The Sporting News and UPI.
In 1961, his numbers fell with Sam Etcheverry at quarterback, posting 44 receptions for 591 yards and 9 touchdowns. The next year Charley Johnson took over at quarterback and he finished with 63 receptions (second on the league) for 1,158 yards (second on the league), with an 18.4 average per reception and 7 touchdowns.
On November 4, 1962, Randle had at the time the second best game statistically by a wide receiver in NFL history as he caught 16 passes for 256 yards in a game against the New York Giants. He finished the 1962 season with 63 receptions for 1,158 yards and eight touchdown catches and was named second-team All-Pro by UPI.
Randle once again passed the 1,000-yard receiving mark in 1963, finishing with 51 receptions for 1,014 yards and 12 touchdowns (fourth on the league).
In 1964, he suffered a serious shoulder separation and was lost for the season after the seventh game. At the time he was on pace for third straight 1,000-yard season.
In 1966, he was limited with a fractured hand and although he didn't miss any games, he only recorded 17 receptions for 218 yards and 2 touchdowns.
In 1967, after drafting wide receiver Dave Williams in the first round, the Cardinals traded him to the San Francisco 49ers in exchange for a second round draft choice (#42-Bob Atkins).
He left the Cardinals as the franchise's second all-time leading wide receiver. In 1988, he was named to the All-time Cardinal Team.
In 1967, he appeared in 14 games (10 starts), registering 33 receptions for 502 yards and 4 touchdowns. In 1968, he was released on October 11 after playing in 3 games.
On October 16, 1968, he was signed by the Dallas Cowboys for depth purposes. He appeared in 6 games as a reserve and had one reception for 12 yards.
In 1969, he was acquired by the Washington Redskins and was moved to tight end. He was injured in a preseason game and was placed on the injured reserve list.
Randle finished his career with 65 touchdown receptions in 120 games, currently placing him 12th on the NFL's all-time TD-per-game list (minimum 60 TDs). His 65 TD catches were also the most in the NFL during the 1960s; Don Maynard caught 84 and Lance Alworth caught 77 in the American Football League (AFL).
In 1961, Bing Devine the general manager of baseball's St. Louis Cardinals, asked him to work with his players on improving their running technique, for which future Hall of Famer Lou Brock gave him credit for his success stealing bases.
After his retirement form playing in 1968, Randle became an assistant coach at East Carolina University where, after one season, he became the Pirates' head coach, a job he held from 1971 through 1973. He then spent two years as head coach at his alma mater, the University of Virginia (1974–1975), two seasons at Massanutten Military Academy (1976–1977), and five seasons at Marshall University (1979–1983).
In the 1960s, he began his broadcasting while still playing for the Cardinals. In the mid-1980s, he was active in sports broadcasting, participating in radio broadcasts of college football games as a color commentator in St. Louis, Virginia, and West Virginia. In 1991, he started S-R Sports, a syndicated talk radio network based in Virginia.
Assistant coaches under Sonny Randle who became NCAA or NFL head coaches:Jim Grobe: Ohio (1995–2000), Wake Forest (2001–2013), Baylor (2016)
Bill Stewart: VMI (1994–1996), West Virginia (2008–2010)
Bob Pruett: Marshall (1996–2004)