Barca only needed a draw to seal the title and they made a ideal start when record signing Philippe Coutinho scored with a stylish chipped shot in the seventh minute while Messi doubled their lead in the 38th by volleying home an outrageous cross by Luis Suarez.
The Argentinian wizard's speed of thought and feet around the box helped him to yet another hat-trick - the 46th of his career.
Barca did not include his name, or the names of the players that left the club during the winter transfer window, including Arda Turan (İstanbul Başakşehir) and Javier Mascherano (Hebei China Fortune), on their celebratory T-shirt.
Madrid are now focusing on their Champions League clash with Bayern Munich.
Messi now has 32 league goals, more than anyone else in Europe's major leagues, and has also contributed 12 assists this campaign.
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When asked what Lopez's secret was following Friday's win at home to Sevilla, Morales said it was simple, "he told us to go out and enjoy ourselves".
"It was a very special title for all of us because we are yet to lose any matches".
Nobody wants to be the forgotten man in football, but Gerard Deulofeu was certainly feeling left out when Barcelona released a commemorative shirt following their LaLiga title triumph.
I am really happy to have won this league title.
Not only did it take place in the middle of a long weekend, when many locals leave the city, but Barca fans are still reeling from their shock elimination by Roma in the Champions League quarter-finals. "There are no words when you receive so much love from people and even more so in hard moments for them [given Deportivo's relegation]".
"It's been an nearly flawless season for us in the league", midfielder Sergio Busquets said. "Winning the Champions has that plus, and it would be a great season for us if we win two back-to-back", he added.
Real, winners of the competition in 2014, 2016 and 2017, are firm favourites to make the Kiev final having won 2-1 in Germany last week.