Nanostructured CaCO3 modified sewage sludge biochar (CMSSB) was successfully fabricated for efficient removal of Cd(II) from aqueous solutions. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses indicated that the loaded CaCO3 mainly existed in the form of dispersive calcite nanoparticles, and the loading of calcite nanoparticles had a slight effect on the morphology of the sewage sludge biochar (SSB). The adsorption capacity of the obtained CMSSB for Cd(II) based on the Langmuir model is 36.5 mg g−1, which was nearly three times higher than that of the pristine SSB. The adsorption process can be well described by the Elovich model, and the initial adsorption rate of the CMSSB is faster than that of the SSB. The Cd(II) adsorption mechanism on the CMSSB involves ion-exchange and precipitation reactions between heavy metal ions and calcite nanoparticles and biochar. The present results suggested that the as-prepared CMSSB is an efficient and economic adsorbent for environmental heavy metal remediation.