Cancer has remained one of the most indomitable conundrums for scientists over centuries due to its multifarious etiology. While improved therapeutic and diagnostic approaches have commendably augmented the rate of survival of cancer patients, a holistic riddance from the ailment is still implausible. Hence, further explorations to scout for novel strategies of cancer therapy and diagnosis are necessary. Theranostics (amalgamation of therapy and diagnostics) has emerged as one of the avant-garde strategies, which provides a two-pronged advantage in cancer management. This integrative approach has found immense relevance in light of nanotechnology. Nanoparticles can be customized (loaded with a mélange of therapeutic drugs and diagnostic probes) to develop theranostic properties, thereby constructing nanotheranostic agents. These nano-composites are lucrative tools for cancer cell obliteration and simultaneous monitoring of the drug action, and can also be tailored for targeted drug delivery. Nanotheranostic agents have emerged as a prudent ploy for synchronized cancer intervention and detection of the ‘route and reach’ of the drugs. In this review, we discuss the diversified state-of-the-art facets of theranostic nanoparticles, including various nanoparticle-based platforms as well as the plethora of reported therapeutic drugs, aptamers, markers and diagnostic molecules that have found use in the precincts of nanotheranostics.