The Catalan giants cruised to a 4-1 victory at Benito Villamarin Stadium, with Luis Suarez notching Barca's other goal to equal Diego Forlan as the joint-highest Uruguayan in La Liga history.
Messi slammed home a 25th-minute free-kick to claim a 1-0 lead before firing in two clinical finishes from close range, including a delightful chip over Betis goalkeeper Pau Lopez for his third, to round off a stunning performance and bag his 33rd hat-trick in the Spanish top flight.
Real Madrid have struggled considerably since his departure having already sacked two managers in Julen Lopitagui and Santiago Solari, crashed out of both the Champions League and the Copa del Rey and effectively conceded the La Liga title.
Barca now have a 10-point lead over Atletico Madrid and a 12-point lead over Real, and their talisman Messi has played a considerable role in their dominant title defence.
The Argentina international has now scored 27 league goals - more than anyone else in Europe's top five leagues this term.
Remarkably, he has also scored more direct free-kick goals (four) and more goals from outside the box (seven) than any of his competitors those competitions.
But while Messi enjoyed a landmark night on Sunday evening, Barcelona did not have everything their own way despite the final score.
The league leaders only had 43.9 per cent of possession which is the lowest share of the ball they have had in any La Liga game since the 2004-05 campaign.
They also only registered three more shots than their opponents - 16 compared to Betis' 13 - although only three of the home side's efforts hit the target.
Should Ernesto Valverde's side win that game, it could effectively tie up the league title with seven games to spare.