We present the quasi-stellar object (QSO) luminosity function (LF) of the completed 2dF-SDSS LRG and QSO (2SLAQ) survey, based on QSOs photometrically selected from Sloan Digital Sky Survey (SDSS) imaging data and then observed spectroscopically using the 2dF instrument on the Anglo-Australian Telescope. We analyse 10 637 QSOs in the redshift range 0.4 <z <2.6 to a g-band flux limit of 21.85 (extinction-corrected) and an absolute continuum magnitude of Mg(z = 2) <-21.5. This sample covers an area of 191.9 deg 2. The binned QSO LF agrees with that of the brighter SDSS main QSO sample, but extends a??2.5 mag fainter, clearly showing the flattening of the LF towards faint absolute magnitudes. 2SLAQ finds an excess of QSOs compared to the 2dF QSO Redshift Survey at g > 20.0, as found previously by Richards et al.