On 14 February 2018, Mané scored his first hat-trick for Liverpool in a 5–0 away win against Porto in the round of 16 first leg of the 2017–18 UEFA Champions League. In doing so, he became only the second player to score an away hat-trick for the club in Europe. Later, with a goal in the 3–0 win over AFC Bournemouth on 14 April, he overtook Demba Ba's record of 43 to become the highest scoring Senegalese in Premier League history.
On 22 November 2018, Mané signed new long-term deal with the Reds. On 10 March 2019, Mané scored twice in a 4–2 win over Burnley, the second of which was his 50th competitive goal for Liverpool. His goals also saw him become only the fifth Liverpool player to score in six consecutive home Premier League appearances after Michael Owen, Fernando Torres, Luis Suárez and Salah. Three days later, he scored twice more in a 3–1 win over Bayern Munich to help Liverpool progress to the quarter-finals of the Champions League. In doing so, he became the club's record goalscorer away from home in the competition with seven goals to his name. During Liverpool's next match, he broke another of Ba's records to become the Senegalese player with the most goals scored in a single Premier League season, after scoring his 17th goal for the campaign in a 2–1 win over Fulham. On 20 April, he was one of six players nominated for the PFA Players' Player of the Year award alongside teammate Virgil van Dijk. He was also named in the PFA Team of the Year alongside Liverpool teammates, Trent Alexander-Arnold, Andrew Robertson and Van Dijk.
In May 2018, Mané was named in Senegal's 23-man squad for the 2018 FIFA World Cup in Russia. He scored the opening goal in a 2–2 draw against Japan in the group stage. Mané started all three of Senegal's group matches as they were eliminated after the first stage, finishing below Japan on fair play points.