This paper investigates the patterned co-occurrences, and strategic-pragmatic implications of selected modality and evidentiality markings in Nigerian Senate debates (NSD). The data for the study comprised a 1.9-million-word corpus of NSD, which was analysed quantitatively and qualitatively. The quantitative analysis explored corpus the methodologies of concordancing and collocation implemented on AntConc 3.5.8; whereas, the qualitative dimension undertook a contextual analysis of selected data indicating the strategic-pragmatic implications of modality and evidentiality markings in NSD. A key finding indicates how legislators rely on these markings to strategically invoke institutional responsibilities/ obligations and attempt to sound argumentatively superior during plenary sessions. The paper has implications for understanding how Nigerian legislators carry out their discursive activities of debating, negotiating and positioning during plenary sessions. Moreover, it makes a methodological contribution to corpus linguistic studies in Nigeria by its use of the collocation tool of AntConc.