Endophytic Beauveria bassiana (Balsamo-Crivelli) Vuillemin can promote plant growth and health and protect them against herbivores. Two endophytic strains of B. bassiana, BS195 (isolated from soil) and BNE20 (isolated from cucumber), were used by foliar spray and root soaking to evaluate B. bassiana ability to colonize cucumber plants and promote their growth under stressful greenhouse conditions in two separate experiments, as well as its efficacy against Liriomyza sativae Blanchard in a controlled setting. The results showed that the effects significantly depended on the inoculation method and fungal strain. Both B. bassiana strains colonized endophytically the tissues of all cucumber plant parts 30 days post-inoculation, with root soaking being significantly better than foliar spray. The present study showed that the application of B. bassiana BS195, mainly through root soaking, enhanced many growth and health parameters, including plant height, root length, number of leaves, leaf area, fresh and dry weight, the content of dry matter, and the total phenolic content. Cucumber plant treatment with B. bassiana significantly reduced the infestation, severity, number of pupae, and adult emergence of L. sativae after 35 and 51 days of adult release with greater efficiency with the root soaking method. We conclude that introducing B. bassiana through root soaking seems to be effective in stimulating plant growth, and can be a promising technique in controlling L. sativae populations on cucumber plants.