The proper design of near-infrared light-absorbing agents enables efficient optoacoustic imaging-guided phototherapy. In particular, several croconaine-based organic agents with excellent optical properties have been recently reported for this purpose. However, most of them absorb light below 800 nm, limiting deep-tissue imaging applications. To this end, we utilized a recently described novel croconaine derivative (CR880) to develop CR880-based nanoparticles (CR880-NPs) for effective in vivo delivery, deep tissue optoacoustic imaging and photothermal therapy applications. Radicals and strong π-πstacking in CR880 result in an 880 nm absorption peak with no blue-shift upon condensing to the solid phase. DSPE-PEG2000-formulated CR880-NPs exhibited high optoacoustic generation efficiency and photostability, and could be visualized in the tumors of three different mouse tumor models (breast, brain, and colon tumor) with high image contrast. The high photothermal conversion efficiency of CR880-NPs (∼58%) subsequently enabled efficient in vivo tumor elimination using a low energy laser, while remaining biocompatible and well-tolerated. This work introduces a promising novel agent for cancer theranostics of challenging deep-seated tumors.