Additive manufacturing is an increasingly disruptive manufacturing technique enabling significantly expanded freedom of design and lower process complexity. Challenges associated with quality monitoring and control, especially internal defect features such as pores, have been recognized as critically important aspects impacting toward mechanical and fracture behavior. Understanding how these defects evolve under loading is important knowledge to assess component reliability and life cycle. Therefore, understanding the correlations of failure mechanisms and defect properties as well as their in-situ development in commonly used materials is an important milestone and appears to be imperative to the adoption of AM techniques in engineering applications. This work employs in-situ tensile testing in combination with X-ray computed tomography to provide 4D insights into porosity evolution. L-PBF 316L samples were designed after E8/E8M standards and manufactured with suboptimal process parameters to create specified lack of fusion defects. Samples were imaged on several occasions throughout the interrupted uniaxial tensile testing procedure. Results were subsequently visualized with digital 3D models and correlated to post-mortem fractography. High porosity with differing morphology types was detected and visualized in the base samples. Pore evolution was minimal in the projected elastic deformation phase and more noticeable in the projected plastic deformation phase. Smaller pores under 100 µm in diameter showed only little growth and slight morphology changes, whereas the development was more pronounced for larger pores over 100 µm in diameter, which showed significant growth and high tendencies toward irregularity.