Both Marega and Marítimo goalkeeper José Sá were on the cusp of a move to Sporting Clube de Portugal in January 2016, but it was hijacked by FC Porto, who signed the pair on contracts lasting to 2020; Marega's buyout clause was set at €40 million.
He made 13 appearances in his first campaign at the Estádio do Dragão – mostly as a substitute – and scored once in a 2–0 home win over Gil Vicente F.C. in the Taça da Liga on 2 March.
His early poor performances drew vocal criticism from some Porto fans, and he took training from a friend on how to become mentally resilient.

On 20 July 2016, Marega was loaned to Vitória de Guimarães for the upcoming season.
He made his debut a month later in a 2–0 win against his former team, Marítimo, scoring the second goal, and on 30 October, he scored all three goals in a 3–0 win against Rio Ave F.C. to reach 10 goals from 8 games.
On 4 November, he received a straight red card in the first half-hour of a 2–1 home win over C.D. Nacional for striking Nuno Sequeira, receiving a three-match ban.

On his return to Porto, Marega scored twice in the opening game of the 2017–18 season, a 4–0 home win over Estoril, as a first-half substitute for Tiquinho.
He was part of a three-pronged attack made of African players, alongside the Cameroonian Vincent Aboubakar and Yacine Brahimi of Algeria.

He scored 14 league goals in 14 starts, and reportedly began to attract the interest of Premier League sides Manchester United and Chelsea in January 2018.
Porto won the league for the first time in five years and Marega was their top scorer (third overall behind Jonas and Bas Dost) with 22 goals.

In November 2018, Marega was awarded the Dragão de Ouro (Golden Dragon) as Porto's best player of the calendar year.
Having not previously scored in a European match, Marega scored a goal in six consecutive appearances in the 2018–19 UEFA Champions League, ending with one in a 3–1 win over A.S. Roma, that put Porto in the quarter-finals for the first time in four years.

On 16 February 2020, after scoring the winning goal on his return to Vitória, Marega gave the middle finger to the home fans who had been racially abusing him.
The insults continued after this incident and in response, he walked out of the game, and was subsequently substituted.
His reaction to the abuse was praised by the Portuguese press, with A Bola newspaper giving Marega a perfect 10 rating in its player ratings.
He scored in a 2–0 home win over Sporting on 15 July that year, as his team won the title with two games left to play.
Both Marega and Marítimo goalkeeper José Sá were on the cusp of a move to Sporting Clube de Portugal in January 2016, but it was hijacked by FC Porto, who signed the pair on contracts lasting to 2020; Marega's buyout clause was set at €40 million. He made 13 appearances in his first campaign at the Estádio do Dragão – mostly as a substitute – and scored once in a 2–0 home win over Gil Vicente F.C. in the Taça da Liga on 2 March. His early poor performances drew vocal criticism from some Porto fans, and he took training from a friend on how to become mentally resilient.
On 20 July 2016, Marega was loaned to Vitória de Guimarães for the upcoming season. He made his debut a month later in a 2–0 win against his former team, Marítimo, scoring the second goal, and on 30 October, he scored all three goals in a 3–0 win against Rio Ave F.C. to reach 10 goals from 8 games. On 4 November, he received a straight red card in the first half-hour of a 2–1 home win over C.D. Nacional for striking Nuno Sequeira, receiving a three-match ban.
On his return to Porto, Marega scored twice in the opening game of the 2017–18 season, a 4–0 home win over Estoril, as a first-half substitute for Tiquinho. He was part of a three-pronged attack made of African players, alongside the Cameroonian Vincent Aboubakar and Yacine Brahimi of Algeria.
He scored 14 league goals in 14 starts, and reportedly began to attract the interest of Premier League sides Manchester United and Chelsea in January 2018. Porto won the league for the first time in five years and Marega was their top scorer (third overall behind Jonas and Bas Dost) with 22 goals.
In November 2018, Marega was awarded the Dragão de Ouro (Golden Dragon) as Porto's best player of the calendar year. Having not previously scored in a European match, Marega scored a goal in six consecutive appearances in the 2018–19 UEFA Champions League, ending with one in a 3–1 win over A.S. Roma, that put Porto in the quarter-finals for the first time in four years.
On 16 February 2020, after scoring the winning goal on his return to Vitória, Marega gave the middle finger to the home fans who had been racially abusing him. The insults continued after this incident and in response, he walked out of the game, and was subsequently substituted. His reaction to the abuse was praised by the Portuguese press, with A Bola newspaper giving Marega a perfect 10 rating in its player ratings. He scored in a 2–0 home win over Sporting on 15 July that year, as his team won the title with two games left to play.
Moussa Marega