Geoffrey Gilbert came joined Sir Thomas Beecham's London Philharmonic Orchestra in London in 1933. He was the principal flute of the LPO at the age of 19 and held this position until the outbreak of World War II in 1939, when he volunteered to join the Coldstream Guards. He served with the Guards throughout the war. He rejoined the London Philharmonic and became a teacher at the Guildhall School of Music. In 1948, he founded the Wigmore Ensemble in collaboration with other woodwind players of that generation including Jack Brymer, Terence MacDonagh and Gwydion Brooke.
In 1948, Gilbert joined the BBC Symphony Orchestra under Sir Adrian Boult. Sir Malcolm Sargent also conducted the BBC's principal orchestra until his resignation in 1952. He rejoined the Royal Philharmonic Orchestra in 1957 and played regularly until 1961. After this time he was the guest principal with the London Symphony Orchestra on many occasions. This led to his long commitment to Stetson University, and his move to Deland, Florida, in 1969.