During the past decade, investments in large-scale irrigation development in sub-Saharan Africa (SSA) have come back. Given past experiences, this revival is controversial. This paper examines whether large-scale irrigation construction in SSA is economically viable by estimating how much it would cost if the Mwea Irrigation Scheme in Kenya, one of the best performing irrigation schemes in SSA, were to be constructed today. The results show that constructing the Mwea Scheme today may be economically viable if the shadow price of rice is as high as the world price that prevailed during the mini-rice crisis in 2008–2013; however, the viability is marginal, not robust. There is certainly untapped physical potential in SSA for large-scale irrigation development, but the economically viable potential remains limited. International donor agencies and national governments wanting to construct large-scale irrigation projects are recommended to assess seriously whether their plan is economically profitable.