Contrary to the expectations and primarily due to stellar Lionel Messi performances, Barcelona was en route to its third continental treble until May 7 when it infamously lost to Liverpool 0–4 in the second leg of the Champions League semi-finals, having been up 3–0 after the first game.

The league title was secured earlier on April 27 and Barça advanced to its sixth consecutive Copa del Rey final on February 27.

On 3 June, Barcelona and defender Samuel Umtiti reached an agreement to extend the player's contract for a further five seasons through to 2022–23 with a release clause of €500 million.

[3] On 8 July, Barcelona announced that they had reached an agreement with Guangzhou Evergrande for the loan transfer of Paulinho for one season, with a subsequent purchase option for the Chinese club.

[10] On 3 August, Barcelona announced that they had reached an agreement with Bayern Munich for the transfer of Arturo Vidal to the Catalan club for the next three seasons for a fee of €18 million.

[14] On 12 August, Barcelona defeated Sevilla 1–2 in the Spanish Super Cup at the Stade Ibn Batouta in Morocco; goals from Gerard Piqué and Ousmane Dembélé handed the Catalans their 13th Supercopa de España title.

[15] On 16 August, Barcelona announced that they had reached an agreement for the transfer of Marlon to the Italian club Sassuolo for an initial fee of €6 million, including a buy-back clause for the Catalans.

Another great performance of Messi as he managed his record-breaking 8th Champions League hat-trick and Dembélé notched the remaining goal from a solo effort to complete another victory for the Blaugrana side.

Valverde's men secured an important victory in a classic, end-to-end match in London to maintain their perfect start in the Champions League group stage.

Four goals and a sensational performance by Ter Stegen allowed Barça to snatch first place back from the leaders on a night that Leo Messi went off injured.

Rafinha and Jordi Alba's superb goals left the Catalans flying high in Champions League Group B with the maximum points at the halfway stage.

[28] On 28 October, in the first El Clásico of the season, and the first since 2007 not to feature Messi or Cristiano Ronaldo, Barcelona thrashed Real Madrid 5–1 at the Camp Nou, with Luis Suárez scoring a hat-trick.

[29] On 3 November, Barca defeated Rayo Vallecano 2-3, two goals from Suárez and another from Ousmane Dembélé earned the Blaugranes a late win at Vallecas.

[31] On 11 November, Barca lost 3-4 to Betis, The Andalusians spoiled Messi's return to action who scored 2 goals, with a shock victory in a dramatic encounter at the Camp Nou seeing Rakitic being sent off after picking his 2nd yellow card .

[32] On 24 November, Barca draw Atlético Madrid 1-1, Diego Costa's late header at the Wanda Metropolitano was cancelled out by Ousmane Dembélé after a brilliant pass of Messi in the final minute of normal time.in addition both Sergi Roberto and rafinha got injured after the game against Atlético [33] On 28 November, Barca defeated PSV Eindhoven 1-2, Goals from a sensational Messi and Piqué clinched the points that ensure top spot in Champions League Group B with a game in hand.

[34] On 2 December, Barcelona defeated Villarreal 2-0 with goals from Gerard Piqué and Carles Aleñá, as well as a great all-round team performance which ensured the win and a clean sheet against worthy opponents.

[35] On 8 December, Barcelona defeated Espanyol 0-4 with two sensational free kicks from Leo Messi, plus goals from Dembélé and Luis Suárez which brought derby delight and another week at the top of the table.

The win ensured Barca remained on top of the table, three points ahead of Atletico Madrid, heading into the winter break.

[41] On 10 January, Barcelona lost to Levante 2-1 in Copa del Rey round of 16, Philippe Coutinho converted a penalty five minutes from the end.

[47] On 23 January, Barcelona announced that they had reached an agreement with Ajax for the transfer of Frankie De Jong who will be joining the Catalan club from 1 July 2019.

Phil Coutinho nets a brace, while Ivan Rakitic, Sergi Roberto, Luis Suárez and Leo Messi notch a goal each.

[56] On 23 February, Barça won Sevilla 2-4, Lionel Messi's stunning hat-trick against his favourite opponent, and Luis Suarez's late goal secured the points for the Blaugrana who twice went behind.

Leo Messi posted yet another legendary hat-trick performance, Luis Suárez added the other, and Barça fly into a ten-point lead in La Liga.

[68] A thriller of an encounter against Villarreal on 2 April found Barça grab a point in a 4-4 draw after two late goals from Messi and Suárez.

[69] On 6 April, Barça won against Atlético de Madrid at the Camp Nou 2-0, goals scored by Luis Suarez and Lionel Messi, a thriller of a match that saw Spanish centre forward Diego Costa being sent off the field after receiving a red card.

An incredible performance by Messi who scored two first-half goals with Coutinho adding a second-half rocket to qualify Barça for their eighth Champions League semi-final in the last 12 seasons.

This loss marked the end of the season for FC Barcelona who won two trophies (La liga and Supercopa de España) out of the possible four, despite having been close to winning them all up until 7 May.

[117] The Blaugrana finished their pre-season preparations with the annual Joan Gamper Trophy match against Boca Juniors of Argentina at the Camp Nou on 15 August.

[121] For the first time in the tournament history, it was a single match hosted in a neutral venue at the Stade Ibn Batouta in Tangier, Morocco.