The performance of field-effect transistors based on single-walled carbon nanotube (SWCNT) networks depends on the electrical percolation of semiconducting and metallic nanotube pathways within the network. We present voltage-contrast scanning electron microscopy (VC-SEM) as a new tool for imaging percolation in a SWCNT network with nano-scale resolution. Under external bias, the secondary-electron contrast of SWCNTs depends on their conductivity, and therefore it is possible to image the preferred conduction pathways within a network by following the contrast evolution under bias in a scanning electron microscope. The experimental VC-SEM results are correlated to percolation models of SWCNT-bundle networks.