His elder brother Toyoteru YAMAUCHI (thirteenth lord), Toyoatsu YAMAUCHI (fourteenth lord) died in succession in 1848 and he was seen as the successor as a younger brother but since he was only 3 years old, Toyonobu (Yodo) YAMAUCHI, who was from a branch line, became the family head.
嘉永元年（1848年）に兄の山内豊熈（第13代藩主）、山内豊惇（第14代藩主）が相次いで死去したため、弟に当たることから後継者と目されたが、わずか3歳の幼少だったため、家督は分家出身の山内豊信（容堂）が継承することとなった。