Nanoparticles with high aspect ratios have favorable attributes for drug delivery and bioimaging applications based on their enhanced tissue penetration and tumor homing properties. Here, we investigated a novel filamentous viral nanoparticle (VNP) based on the Pepino mosaic virus (PepMV), a relative of the established platform Potato virus X (PVX). We studied the chemical reactivity of PepMV, produced fluorescent versions of PepMV and PVX, and then evaluated their biodistribution in mouse tumor models. We found that PepMV can be conjugated to various small chemical modifiers including fluorescent probes via the amine groups of surface-exposed lysine residues, yielding VNPs carrying payloads of up to 1600 modifiers per particle. Although PepMV and PVX share similarities in particle size and shape, PepMV achieved enhanced tumor homing and less nonspecific tissue distribution compared to PVX in mouse models of triple negative breast cancer and ovarian cancer. In conclusion, PepMV provides a novel tool for nanomedical research but more research is needed to fully exploit the potential of plant VNPs for health applications.