Post-transcriptional regulation of gene expression occurs by multiple mechanisms, including subcellular localization of mRNA and alteration of the poly(A) tail length. These mechanisms play crucial roles in the dynamics of cell polarization and embryonic development. Furthermore, mRNAs are emerging therapeutics and chemical alterations to increase their translational efficiency are highly sought after. We show that yeast poly(A) polymerase can be used to install multiple azido-modified adenosine nucleotides to luciferase and eGFP-mRNAs. These mRNAs can be efficiently reacted in a bioorthogonal click reaction with fluorescent reporters without degradation and without sequence alterations in their coding or untranslated regions. Importantly, the modifications in the poly(A) tail impact positively on the translational efficiency of reporter-mRNAs in vitro and in cells. Therefore, covalent fluorescent labeling at the poly(A) tail presents a new way to increase the amount of reporter protein from exogenous mRNA and to label genetically unaltered and translationally active mRNAs.