Workers are increasingly exposed to nanoparticles, mostly via inhalation. Respiratory protection is recommended as an additional control measure. Particulate respirators are certified for protection against micro-sized particles, where a most penetrating particle size (MPPS) of 100–400 nm is assumed. Commonly used N95 respirators are certified by the National Institute for Occupational Safety and Health after passing a 95% collection efficiency test. Electret media used in respirators have been demonstrated to be shifting the MPPS to a nanosized region. Experimental studies have therefore been conducted to assess N95 respirator penetration specifically by nanoparticles. This systematic review and meta-analysis was aimed at systematically reviewing these studies and meta-analysing the mean penetration percentage (PP). The review was conducted following a Preferred Reporting Items for Systematic Reviews and Meta-Analyses guideline. Fourteen studies were selected to be reviewed qualitatively, while 13 of these with 29 data points were included in the meta-analysis. Sensitivity analysis was performed based on a respirator mounting protocol, while subgroup analysis was done for aerosol dispersity and repeated for the respirator mounting protocol. The size range of particles used across the reviewed studies was 1 nm–10 μm. The MPPS for all studies was in the nanosized particle range, with the lowest at approximately 39 nm. The estimated mean PP was between 1 and 6%, exceeding the 5% guideline threshold for four of the studies. All the meta-analysed mean PPs were however below the 5% guideline. This means that the N95 respirators may be effective for nanoparticles in workplaces, but subject to factors including respirator characteristics and particle dispersity.