Context : The nature of the hard X-ray source XSS J12270-4859 is still unclear .
It was claimed to be a possible magnetic Cataclysmic Variable of the Intermediate Polar type from its optical spectrum and a possible 860 s X-ray periodicity in RXTE data .
However , recent observations do not support the latter variability , leaving this X-ray source still unclassified .

Aims : To investigate its nature we present a broad-band X-ray and gamma ray study of this source based on a recent XMM-Newton observation and archival INTEGRAL and RXTE data .
Using the Fermi /LAT 1-year point source catalogue , we tentatively associate XSS J12270-4859 with 1FGL J1227.9-4852 , a source of high energy gamma rays with emission up to 10 GeV .
We further complement the study with UV photometry from XMM-Newton and ground-based optical and near-IR photometry .

Methods : We have analysed both timing and spectral properties in the gamma rays , X-rays , UV and optical/near-IR bands of XSS J12270-4859 .

Results : The X-ray emission is highly variable showing flares and intensity dips .
The flares consist of flare-dip pairs .
Flares are detected in both X-rays and UV range whilst the subsequent dips are present only in the X-ray band .
Further aperiodic dipping behaviour is observed during X-ray quiescence but not in the UV .
The broad-band 0.2–100 keV X-ray/soft gamma ray spectrum is featureless and well described by a power law model with \Gamma =1.7 .
The high energy spectrum from 100 MeV to 10 GeV is represented by a power law index of 2.45 .
The luminosity ratio between 0.1–100 GeV and 0.2–100 keV is \sim 0.8 , indicating that the GeV emission is a significant component of the total energy output .
Furthermore , the X-ray spectrum does not greatly change during flares , quiescence and the dips seen in quiescence .
The X-ray spectrum however hardens during the post-flare dips , where a partial covering absorber is also required to fit the spectrum .
Optical photometry acquired at different epochs reveals a period of 4.32 hr that could be ascribed to the binary orbital period .
Near-IR , possibly ellipsoidal , variations are detected .
Large amplitude variability on shorter ( tens mins ) timescales are found to be non-periodic .

Conclusions : The observed variability at all wavelengths together with the spectral characteristics strongly favour a low-mass atypical low-luminosity X-ray binary and are against a magnetic Cataclysmic Variable nature .
The association with a Fermi /LAT high energy gamma ray source further strengths this interpretation .