Fatigue crack growth tests have been conducted on S355 G10+M structural steel which is widely used in the fabrication of offshore structures. Fracture mechanics tests have been performed on compact tension specimens with the crack tip located in the heat affected zone. All tests were performed at room temperature in air and the obtained results are compared with the literature data available on a range of offshore structural steels and also the recommended BS7910 trends using the 2-stage law and simplified law. The specimen orientation, with respect to the location of the extraction within the welded plate, has also been examined and discussed in this work. Residual stress measurements have been performed prior to testing by using the neutron diffraction technique. Finally, a numerical model has been developed in order to calculate the effective stress intensity factor range in the presence of residual stresses. The results have shown that the residual stresses play a key role in the fatigue life of the welded structures, especially in the near threshold region.