Messi opened the scoring in the first half with an arrowed free kick into the top corner and added Barca's second just before the break after a brilliant no-look back-heel assist from Luis Suarez.
Suarez, who missed two brilliant chances to further extend Ernesto Valverde's side lead, eventually added the third with a fine individual effort just after the hour mark.
The win moves Barca 10 points clear of second-placed Atletico Madrid, who lost at Athletic Bilbao on Saturday, and a seventh league title in 10 years is now on the horizon.
And with Messi in this kind of form, they must be favourites for the Champions League and the Copa del Rey, too. This was another sensational hat trick for his portfolio. He now has 29 league goals in just 24 starts and has already scored 39 goals in all competitions. There's so much more to him than just his goals, too -- he's also set up 21 in all competitions.
Barca will hope an injury which forced Suarez off late on proves nothing serious. The Uruguayan looked in a lot of pain as he sought treatment on the sidelines. The international break, which starts tomorrow, means he will be allowed plenty of time to recover before Barca's next game against Espanyol at the end of March.
Manager rating out of 10
8 -- Valverde was one of the big winners on Sunday. After losing to Betis at Camp Nou earlier in the season, he came up with the perfect revenge plan at the Benito Villamarin. From Marc-Andre ter Stegen's clever passing over the home side's press, to Barcelona's own intelligent pressing game, he didn't miss a single detail.
Player ratings (1-10; 10 = best. Players introduced after 70 minutes get no rating)
GK Marc-Andre ter Stegen, 7 -- A busy night with his feet. he provided the base to several Barca attacks, lofting the ball over the pressing Betis midfielders, often to Jordi Alba who was hurtling forward on the left. Could do little about Moron's well-taken goal.
DF Sergi Roberto, 6 -- Was targeted by Betis earlier on as the home side found plenty of joy down Barca's right. Improved as Barca took control of the game, eventually moving from right-back into midfield in the second half.
DF Gerard Pique, 7 -- Did well against a Betis side eager to press Barca's defenders, keeping calm on the ball. Is having an excellent season and will now enjoy some time off after retiring from international football
DF Jordi Alba, 7 -- Was caught out for the Betis goal but other than that was very good in defence and attack. Made two key interventions in his own box and exploited the space in front of him on the left flank. Set up Messi's third goal.
MF Sergio Busquets, 7 -- Started with a misplaced pass which gifted Betis a corner but soon got his act together. An assured performance which often saw him pushing further forward than usual.
MF Ivan Rakitic, 7 -- A quieter performance than in recent weeks but an effective one. Chipped in in defence and attack, linking well with the forwards in the absence of any natural wide players.
MF Arthur, 7 -- One of his most box-to-box performances since joining the club. With four midfielders picked, as opposed to three, it meant he had to join in more attacks. Won the free kick which led to the opening goal.
FW Arturo Vidal, 7 -- His time at Barca has been characterised by his fight but he showed quality here. A fine pass opened up the home defence in the first half, but Suarez missed the chance to cap the move with a goal. Denied twice by good saves from Lopez.
FW Lionel Messi, 10 -- You can more or less copy and paste what's been said already this season. Has now scored two more goals on 11 occasions this season and has netted four hat-tricks. Can score free kicks, can finish off free-flowing team moves, can score chips from the edge of the box... all while dropping deep and creating play, too.
FW Luis Suarez, 8 -- Almost the prototype Luis Suarez performance. Missed two chances like he was a non-league striker but produced two moments of pure brilliance. The no-look, back-heel assist for Messi was good, the powerful run, which saw off three Betis players and ended with a goal, was probably better.
DF Nelson Semedo, 6 -- Came on in the second half and was booked for diving to try and win a penalty.
MF Carles Alena, N/R -- Only introduced in the 89th minute.
MF Philippe Coutinho, N/R -- Brought on even later than Alena, with just 45 seconds of normal time left. That in itself raises more questions about his role in this Barca side.