Liquid chromatography-mass spectrometry (LC-MS)-based proteomics approaches have been widely used to identify residual host-cell proteins (HCPs) in support of process and product characterization for protein therapeutics. Particularly, these methods can provide a general and unbiased approach for the detection of HCPs and may generate critical information on HCPs that are outside the coverage provided by a conventional immunoassay. A significant technical hurdle for HCP analysis is the overwhelmingly large background of biotherapeutic that obscures HCP detection and quantification. In this work, we developed a method that relies on hydrophilic interaction chromatography (HILIC) for HCP enrichment followed by in situ concentration and digestion prior to LC-MS analysis. This approach has enabled detection of HCPs in a drug substance that were not observed in other conventional flow rate LC-MS strategies. For example, 28% of HCPs identified in NISTmAb (20 out of 71) were not previously published or identified by established methods such as the native digestion technique. For an IgG1 protein spiked with 1000 ppm HCP standards, we detected 83 HCPs, 61 out of which were not identified by the native digestion method. Similar improvement in performance was demonstrated for an Fc-fusion protein therapeutic. Our method can be readily implemented in most protein mass spectrometry laboratories to support process development for protein therapeutics.