The effects of martensite development on lattice strain evolution during the in situ compression of austenitic stainless steels, Type 304L, at ambient and cryogenic temperatures were investigated. Engin-X neutron diffractometer was used to study the change in the lattice strain during the uniaxial compression to 10% strain in situ. The report found no evidence of martensite during the compression test at ambient temperature. Similarly, no martensite was observed at cryogenic temperatures up to the applied load of 200 MPa in the elastic region. Martensite was only observed during the plastic deformation at cryogenic temperatures up to the applied strain of 10%. The presence of martensite in the austenitic stainless steels microstructure reinforces the austenite matrix. This was evident from the decrease in the lattice strain as the deformation temperature decreases.