Messi reached the milestone during a 6-1 victory that kept the Catalan side perfect during the current La Liga season.
300 - Lionel Messi has scored his 300th goal for Barcelona at the Camp Nou (all competitions). Milestone.— OptaJose (@OptaJose) September 19, 2017
After a sluggish start to the match, Messi converted a penalty 20 minutes in to take his 2017 tally to 40 goals in as many games.
The 30-year old then scored twice in quick succession in the second half to complete his hat-trick - his second of the season after putting three past Espanyol.
The five-time Ballon d'Or winner was not done there as he added his fourth three minutes from the end to complete the six-goal hammering.
Messi has scored on eight of his last 12 shots in La Liga.
8 - Lionel Messi's last 12 shots on target in La Liga:— OptaJose (@OptaJose) September 19, 2017
And with nine goals already in the league, the Argentine is already looking a decent bet for the Pichichi title.