Argentina's maestro's two goals against Alaves on the last day of the La Liga season cemented his seventh La Liga gold shoe, overshadowing a record he previously held jointly with Telmo Zarra.
It is also the fourth consecutive season, the Barcelona captain leads the league's goal ranking.
It is the first time that the winner of the Pichichi Trophy has scored less than 30 goals since Daniel Guiza of Mallorca 12 years ago.
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Messi ended the season with 25 goals, four more than his closest challenger, Karim Benzema of Real Madrid.
He also recorded 21 assists during the championship campaign, breaking the record 20 previously held by former Barcelona teammate Xavi.
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After Barcelona suffered a shock defeat against Osasuna in their penultimate league match, the very night Real Madrid won the title of champion for the first time since 2017, Messi called his team "weak".
"We did not expect to end this way, but it sums up the year for us," Messi said on Spanish television after the match.
"We have been an erratic and weak team that can be beaten with enough intensity and enthusiasm. We have lost a lot of points that we shouldn't have done and have been very inconsistent."
