The ideal rice phenotype is that of plants exhibiting fewer panicles with high biomass, large grain number, flag leaf area with small insertion angles, and an erected morphology improving light interception. The sunflower transcription factor HaHB11, homeodomain–leucine zipper I, confers increased seed yield and abiotic stress tolerance to Arabidopsis and maize. Here, we report the obtaining and characterization of rice plants expressingHaHB11driven by its promoter or the 35S constitutive one. Transgenicp35S:HaHB11plants closely resembled the ideal high-yield phenotype, whereas those carrying thepHaHB11:HaHB11construct were hard to distinguish from the wild type. The former had an erected architecture, enhanced vegetative leaf biomass, rolled flag leaves with a larger surface, sharper insertion angles insensitive to brassinosteroids, and higher harvest index and seed biomass than the wild type. The combination of the distinct features exhibited byp35S:HaHB11plants, including the increased number of set grains per panicle, supports the high-yield phenotype. We wondered whereHaHB11has to be expressed to achieve the high-yield phenotype and evaluatedHaHB11expression levels in all tissues. The results indicate that its expression is particularly necessary in the flag leaf and panicle to produce the ideal phenotype.