Early in his career, Mahones played with Joe Morris (1948) and Milt Jackson. He served in the Army during the Korean War and then played with Lester Young from 1953 to 1956. Later in the 1950s he toured with the Jazz Modes (whose members included Charlie Rouse and Julius Watkins), Sonny Stitt, and Benny Green. From 1959 to 1964 he played behind Lambert, Hendricks & Ross.
When LHR split, Mahones relocated to Los Angeles where he worked both as a studio musician and as a jazz sideman. He led his own trio, and appeared on recordings by O.C. Smith, Lou Rawls, James Moody, Harold Land and Blue Mitchell, Leon Thomas, Jim Hall, Big Joe Turner, Lorez Alexandria, Benny Carter, Pony Poindexter, Booker Ervin, and Jimmy Witherspoon.
- I'm Shooting High (Prestige, 1963)
- The Great Gildo (Prestige, 1963–64)
- Gildo Mahones Trio (Interplay, 1990)
With Kenny Burrell
With Ted Curson
- Ted Curson Plays Fire Down Below (Prestige, 1962)
With Booker Ervin
With Bennie Green
With Willis Jackson
- Neapolitan Nights (Prestige, 1962)
- Havin' a Ball at the Village Gate
- A Good Git-Together
- Lambert, Hendricks, & Ross!
- At Newport ’63 (RCA, 1963)
- Les Jazz Modes (Dawn, 1957)
- Mood in Scarlet (Dawn, 1957)
- The Most Happy Fella (Atlantic, 1958)
- The Jazz Modes (Atlantic, 1959)
With Frank Wess
- Yo Ho! Poor You, Little Me (Prestige, 1963)
With Jimmy Witherspoon