Context :

Aims : One of the goals of the XMM-Newton survey of the Small Magellanic Cloud is the study of the Be/X-ray binary population .
During one of our first survey observations a bright new transient - XMMU J004814.0-732204 - was discovered .

Methods : We present the analysis of the EPIC X-ray data together with optical observations , to investigate the spectral and temporal characteristics of XMMU J004814.0-732204 .

Results : We found coherent X-ray pulsations in the EPIC data with a period of ( 11.86642 \pm 0.00017 ) s. The X-ray spectrum can be modelled by an absorbed power-law with indication for a soft excess .
Depending on the modelling of the soft X-ray spectrum , the photon index ranges between 0.53 and 0.66 .
We identify the optical counterpart as a B = 14.9mag star which was monitored during the MACHO and OGLE-III projects .
The optical light curves show regular outbursts by \sim 0.5 mag in B and R and up to 0.9 mag in I which repeat with a time scale of about 1000 days .
The OGLE-III optical colours of the star are consistent with an early B spectral type .
An optical spectrum obtained at the 1.9 m telescope of the South African Astronomical Observatory in December 2009 shows H { \alpha } emission with an equivalent width of 3.5 \pm 0.6 Å .

Conclusions : The X-ray spectrum and the detection of pulsations suggest that XMMU J004814.0-732204 is a new high mass X-ray binary pulsar in the SMC .
The long term variability and the H { \alpha } emission line in the spectrum of the optical counterpart identify it as a Be/X-ray binary system .