During his extensive professional career he played for ten different clubs, all in Spain, after emerging through Real Madrid's youth system.

Having started 1999–2000 in the second division, Gerardo was purchased by Valencia CF in January 2000, appearing scarcely for the Che during the campaign but being a starter in the UEFA Champions League final loss to Real Madrid.

Gerardo had his most successful period at Málaga CF, playing five seasons for a side that had four consecutive mid-table positions and also helping them win the 2002 UEFA Intertoto Cup.

[2] After only 12 second-tier games in the second season, the 36-year-old left after his contract was not renewed, and signed for SD Logroñés of Tercera División, retiring two years later.

After retiring, Gerardo founded the 'Gerardo García León Tiki-taka Football Academy' and also acted as youth coach for amateurs Comillas CF.