The study of electromagnetic (EM) wave absorbing materials is a natural response to ever-worsening EM wave pollution in modern days. Several nanomaterials have been explored as wideband, low-thickness, and lightweight microwave absorbing materials (MAMs) for use in both military and civilian realms but require significant improvement. This work presents the synthesis and charcaterization of in situ exfoliated boron nitride coated nickel ferrite (NiFBN) with excellent porous microstructure, using a simple auto-combustion method as well as the fabrication of a NiFBN-multiwalled carbon nanotube (MWCNT)-epoxy-based lightweight, thin nanocomposite for wideband microwave absorption (X-band). With a 2 mm thick sample, the 15-NiFBN-0.75_2mm nanocomposite exhibits effective absorption bandwidth (EAB) of 3.9 GHz and −59.38 dB reflection loss minima (RL_min). Several percentages of boron nitride with nickel ferrite were synthesized using the sol–gel auto-combustion process, and the MWCNT percentage was adjusted for enhanced microwave absorption.