Boolean bent functions which at the same time have a flat nega-Hadamard transform are called bent-negabent functions. The known families of these functions mostly stem from the Maiorana-McFarland class of bent functions and their vectorial counterparts have not been considered in the literature. In this article, we introduce the notion of vectorial bent-negabent functions and show that in general for a vectorial bent-negabent function <inline-formula> <tex-math notation="LaTeX">F\colon {\mathbb {F}} _{2}^{2m} \rightarrow {\mathbb {F}} _{2}^{k} </tex-math></inline-formula> we necessarily have that <inline-formula> <tex-math notation="LaTeX">k \leq m-1 </tex-math></inline-formula>. We specify a class of vectorial bent-negabent functions of maximal output dimension <inline-formula> <tex-math notation="LaTeX">m-1 </tex-math></inline-formula> by using a set of linear complete mappings. On the other hand, we propose several methods (one of which is generic) of specifying vector spaces of nonlinear complete mappings which then induce vectorial bent-negabent functions (whose dimension is not maximal) having a certain number of component functions outside the completed Maiorana-McFarland class. Finally, we derive an upper bound on the maximum number of bent-negabent components for mappings <inline-formula> <tex-math notation="LaTeX">F\colon {\mathbb {F}} _{2}^{2m} \rightarrow {\mathbb {F}} _{2}^{k} </tex-math></inline-formula>, where <inline-formula> <tex-math notation="LaTeX">m \leq k \leq 2m </tex-math></inline-formula>, and identify some families of these functions reaching this upper bound.