During the second half of the 2018–19 Bundesliga campaign, Brandt was re-positioned by new club manager Peter Bosz, shifting from his natural wide position to a more central role in midfield alongside Kai Havertz. His goal contribution increased as a result of the positional change and in February 2019, after scoring twice and assisting a further four goals, he was nominated for the Player of the Month award. He ultimately won the award and in doing so became the first Leverkusen player to claim the accolade. His brace against Mainz 05 at the start of the month also came on the occasion of his 200th appearance for the club across all competitions.
Brandt was Dortmund's transfer target after the 23-year-old scored seven league goals, provided eleven assists and subsequently helped Leverkusen to finish fourth in Bundesliga and secure a Champions League third qualifying round spot for next season. On 22 May 2019, Brandt completed a transfer to Borussia Dortmund on a five-year deal for a reported €25 million after Dortmund activated a release clause in his contract. He arrived at the same time as new teammate Thorgan Hazard, who moved from Borussia Mönchengladbach.