Mario Vrančić became Norwich's third signing of the 2017 summer transfer window when he joined for German side SV Darmstadt 98 on 8th June 2017. The Bosnian international midfielder signed a three year deal for an undisclosed fee.

Mario played youth football for VfR Kesselstadt (1995-2004) before joining 1. FSV Mainz 05. After progressing from their reserve team, he made 9 first team appearances. He was loaned to Rot Weiss Ahlen in June 2009. On his return to Mainz, he was relegated to the reserves, and six months later, he left the club to join Borussia Dortmund II

On 1 July 2012 he joined SC Paderborn 07 for whom he played for in the 2. Bundesliga and Bundesliga until the end of the 2014–15 season. He made 93 league appearances.

On 24 June 2015, he signed for newly promoted side SV Darmstadt 98.He played 45 games in two seasons, scoring six goals. he had played 251 professional games by the time of his transfer to Norwich.

Vrančić has represented Germany at under-17, under-19 and under-20 level. He won 2008 UEFA European Under-19 Football Championship with Germany. In 2015, Vrančić received a green light from FIFA to play for Bosnia and Herzegovina. He made his debut for the Bosnian national team on 6th September 2016 against Andorra.

He made his Norwich debut in the 1-1 draw away to Fulham on the opening day of the 2017/18 season (5th August 2017). He scored his first two goals for City in the 3-1 win at Brentford in the League Cup on 19th September 2017. He ended the season with 39 appearances and 3 goals.

In 2018/19 Vrancic scored 10 often vital goals (e.g. against Sheffield Wednesday and Aston Villa) in 38 games as Norwich won the Championship and promotion to the Premier League. He made 23 appearances the following season, mostly as substitute, as Norwich were relegated to the Championship.

Vrancic departed Norwich at the end of the 2020/21 season when his contract expired. He had made 34 appearances, scoring three goals, during 2020/21 as the Canaries won the Championship with his final appearance for the club coming against Barnsley on 8th May 2021.

On 3rd July 2021 rumours in The Telegraph said that Vrancic had completed a medical and was to be unveiled as a Stoke City player on 5th July 2021. This was indeed confirmed on 5th July 2021.

Vrancic made 35 appearances for Stoke in his debut season, scoring three goals. On 18th June 2022 he joined Croatian side HNK Rijeka on a season-long loan. Vrancic's former Norwich teammate Josip Drmic spent 2021-22 on loan at Rijeka and advised Vrancic on the move. On 14th February 2023 Vrancic signed permanently for Rijeka.

He was loaned to Bosnian side FK Sarajevo on 15th February 2023 and made the move permanent on 4th July 2023.