Talent agglomeration serves as a vital pathway for achieving high-quality economic development. This paper, based on provincial panel data from China spanning 2011–2020, first analyses the impact of talent agglomeration on high-quality economic development from two dimensions: the talent agglomeration scale and effectiveness. Second, with innovation activity as a threshold variable, this paper explores the nonlinear impact of the talent agglomeration scale and effectiveness on economic efficiency improvement and economic structure optimization. This study finds that (1) the main driving force for high-quality economic development within the sample period comes from the talent agglomeration scale, while the promoting role of talent agglomeration effectiveness has not yet passed significant tests. (2) Under different levels of innovation activity, the talent agglomeration scale has a diminishing marginal utility impact on economic efficiency improvement and economic structure optimization; talent agglomeration effectiveness also has different nonlinear effects on economic efficiency improvement and economic structure optimization.