Absorption of pulsed laser light energy at the plasmon resonant wavelength of silica-gold core-shell nanoparticles results in a reshaping of the nanoparticle's metal shell layer. Dramatically distinct and reproducible changes in nanoparticle morphology occur as a function of laser pulse width in the femtosecond versus nanosecond regime and laser fluence. The changes are accompanied by large modifications in the plasmon resonant wavelength and spectrum of the reshaped nanoparticle. At the highest femtosecond pulse energies used, deformation of the silica core is also observed.