In 1978, Tejero, along with Police Captain Ricardo Sáenz de Ynestrillas Martínez [es] and an Army General Staff colonel, whose name was never made public, attempted a coup, known as Operation Galaxia.

Around midnight, when it became clear that no further army units had joined the putsch, King Juan Carlos I gave a nationally televised address denouncing the coup and urging the preservation of law and continuance of the democratically elected government.

[2] Held in jail after the coup attempt, Tejero founded the Spanish Solidarity party to run in the 1982 general election and obtain parliamentary immunity.

[4] Tejero was the last of the coup participants to be released from jail on 3 December 1996, having then served 15 years in the Alcalá de Henares military prison.

In 2006, he wrote to the newspaper Melilla Hoy, calling for a referendum on Spanish Socialist Workers' Party (PSOE) proposals granting a new measure of autonomy to Catalonia.