With Atletico Madrid having won earlier in the day to move level at the top, Barca reasserted their authority as first-half goals from Ousmane Dembele and Messi paved the way for a routine victory at Camp Nou.
Messi was again at the heart of the hosts' best play, his shot being parried to the feet of the grateful Dembele to apply the finish inside the opening 10 minutes.
The Argentina star got in on the act himself in the final minute of the first half as Barca all but sealed the points before the interval.
Barca quickly seized the initiative as Dembele pounced to nutmeg Ruben Blanco after the goalkeeper had kept out Messi's low drive.
The visitors narrowly escaped further punishment when Blanco rushed out to thwart Dembele, with Jordi Alba turning the loose ball towards goal where Nestor Araujo was on hand to intervene.
Marc-Andre ter Stegen was finally called into action in the 24th minute and the Barca keeper proved equal to Maxi Gomez's effort.
Messi doubled Barca's lead late in the half, calmly finishing from the edge of the box after Alba's searching pass had left Celta exposed.
Luis Suarez proved uncharacteristically wasteful when presented with a glorious chance to put the game to bed just past the hour mark, the forward shooting wide of the target with only Blanco to beat.
Blanco had stay sharp to deny Messi a second in a brief goalmouth scramble while Celta, despite enjoying more of the ball, continued to struggle in the final third.
Brais Mendez's effort had Ter Stegen diving low to his left, but that save was as comfortable as Barca's whole evening had been.
What does it mean? Barca go clear again
Barca did not seem to take too kindly to having company at the top of the table after being joined there by Atletico, but this win restored their cushion and provided a fitting end to the year. Celta, meanwhile, remain mid-table.
Magnificent Messi does it again
Having played a significant role in the opener, Messi got himself on the scoresheet before the break in a display that highlighted just what a threat he is, cementing his spot at the top of the LaLiga scoring charts.
Suarez was as industrious as he always is, but while Dembele and Messi both found the back of the net, the Uruguay international's finishing was wayward, failing to find the target with two attempts at goal.
Key Opta Facts:
- Messi has reached 15+ goals in LaLiga for each of the last 11 seasons.
- Barcelona have scored 102 league goals in 2018, more than any other team in the top five European leagues.
- Messi has scored 47 goals in 49 games in 2018 in all competitions, more than any other player from those five divisions.
- Barcelona have kept four consecutive clean sheets in LaLiga for the first time since January.
- Valverde has not lost any of his 16 games as a head coach against Celta in LaLiga (W11 D5).
The two sides can enjoy a festive break now and will return to action in January, with Barca heading to Getafe in their first game of 2019, while Celta host Athletic Bilbao.