The business environment is constantly changing according to the influence of competitive forces and other environmental factors. Firms respond to the conditions surrounding them by adjusting their purpose and shape via deployment of appropriate strategic capabilities to match the environmental challenges and enhance competitiveness. Increasingly many firms have resorted to heavy investments in IT capabilities, to cope with the changing business environment. However, only some firms receive pay offs while many others do not. This study is of the view that the difference in competitiveness of firms with respect to the heavy IT investments is in how the individual firm competence mediates the deployment IT capabilities. However, there is scarcity of information on mediation of firm competence on the deployment of IT capabilities as a source of competitiveness. This study undertook to explore how firm competence mediates the deployment of information technology to build competitiveness among consultancy firms Nairobi County, Kenya. This study tested the null hypothesis that firm competence does not mediate the relationship between IT capabilities and firm competitiveness. This study adopted a positivist philosophy approach, cross-sectional explanatory research design and random sampling method in order to obtain the primary data. From the total population of 265 consultancy firms in Nairobi, a target sample of 200 consultancy firms was picked via Microsoft excel generated random numbers. Data collection was done via structured questionnaires, after which multiple regression analyses were used to analyze the data. External validity of the questionnaire was complied with by adequate sample size, which for this study was 200. The reliability of the research instrument was tested via test-retest method on the same pilot sample and the instrument refined to achieve a Cronbach alpha coefficient of 0.855. The outcome of this study was in line with the theoretical and conceptual predictions. The study found that Firm competence partially mediates the relationship between IT capabilities and firm competitiveness, within the context of consultancy business firms in Nairobi County, and the consultancy firms can strengthen this relationship by increasing the level of email usage by the organization, automation of organizational processes and automation of customer information, which will give rise to better firm competence and ultimately higher level of competiveness. Finally the study recommended that consultancy business firms in Nairobi County should increase the level of email usage by the organization, resulting in better firm competence and subsequently higher level of firm competiveness.