laSexta was founded by Antonio García Ferreras on November 25, 2005 when the station got the broadcast license. Later on December 12, 2005, the station began test broadcasting, shortly before knowing the analog frequencies assigned to Madrid and Barcelona.
On December 23, 2005, the station started broadcasting in Madrid and Barcelona, expanding later to all Spain.
Starting on January 23, 2006 they began broadcasting a promotional video. On February 20, 2006, the station marked the start of content emissions testing. Actual broadcasts started with documentaries (Champions, Natura) and programs dedicated to tuning, like 'Tuning Mania'. From February 22, 2006, laSexta broadcast twelve hours of programming every day.
On March 2, 2006, a football match between Croatia and Argentina was the occasion for the first live broadcast. Five days before the actual date, José Miguel Contreras announced the official starting date, March 27, 2006, on the 'Círculo de Bellas Artes'.
HD logo (2010–2013). laSexta HD was launched on November 1st, 2010 along with La Sexta 2 and La Sexta 3.