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The abundancy of defect sinks in the microstructure of laser powder bed fusion (LPBF) processed austenitic stainless steels was found to be beneficial for helium resistance. In the current study, the influence of the novel microstructure in LPBF processed 304L on the helium bubble growth behaviour was investigated using transmission electron microscopy in samples implanted with He + ion and post-irradiation annealing treated at 600 °C for 1 h. Two variants of LPBF processed 304L samples were used, one in as-built condition and the other solution-annealed. The comparison between the two samples indicated that the helium bubble growth was inhibited and remained stable in the as-built sample but coarsened significantly in the solution-annealed sample. The sub-grain boundaries and oxide nano-inclusions acted as defect sinks to trap helium atoms and inhibited the growth of helium bubble in the as-built sample under the post-irradiation annealing conditions used.