Owing to the high cooling rates and thermal gradients, additive manufacturing (AM) of metals results in the formation of hierarchical microstructures such as melt pools, grains, cellular/dendritic structures, and copious amounts of dislocations. These features govern the complex layer-wise solidification within a melt pool and epitaxial growth of grains between layers which results in the formation of potentially strong textures. In this work, we use laser powder bed fusion (LPBF) technique to produce two differently processed samples from an in-situ alloyed β Ti alloy (bcc crystal structure) with differing textures i.e., a <100> cube texture and a near random texture. We use our newly designed, fully automated 3D electron backscattered diffraction (EBSD)-based large volume 3D microstructure characterization system, ELAVO 3D, to understand the complex solidification and grain orientation selection mechanisms within and across the 3D volume of the melt pools which eventually results in the texture of the bulk part. The 3D observation reveals that grains may extend very long through the microstructure and undergo characteristic crystal lattice rotations which can span several tens of degrees and various rotation axes. The results from this work provide insights to advance the current knowledge on texture formation mechanisms in metal AM.