Sodium lignosulfonate (SL), a byproduct of the pulping industry, was used as a stabilizer for the mineralization of CaCO3. In a calcium acetate–urea–water system, the direct aging of the aqueous solution of calcium acetate and urea resulted in the formation of mixed aragonite and vaterite phases or a pure aragonite phase depending on the aging time. However, SL was introduced into the calcium acetate–urea–water system to markedly stabilize the formation of a thermodynamically unstable vaterite phase. Various morphologies of vaterite structures were observed by adjusting the concentration of urea and SL as well as the aging time. Based on these results, ion exchange, carbonate attacking the calcium(II) ions, aggregations of SL-stabilized primary CaCO3 particles through oriented attachment and Ostwald ripening, as well as mesoscale self-assembly were proposed as mechanisms to elucidate the formation of various morphologies.