A frequent competitor for Poland in the 4×400 metres relay, he has won two medals at the European Athletics Championships and reached the final at the 2016 Summer Olympics.

He also won a relay gold medal at the 2009 European Athletics U23 Championships, running alongside Marcin Sobiech, Pietrzak, and Ciepiela.

[4] This earned his global senior debut at the 2011 World Championships in Athletics,[7] where the Polish team of Kacper Kozłowski, Piotr Wiaderek, Krzewina and Marcin Marciniszyn ran in the relay.

He anchored a team of Kozłowski, Omelko and Pietrzak to take Poland to fourth place in the 4×400 m relay final at the 2014 IAAF World Indoor Championships on home turf in Sopot (Krzewina's highest global finish at that point).

Starting his leg in fourth place, he narrowly overhauled Thomas Jordier in the final straight to win the bronze medals for Poland (setting a personal relay best of 2:59.85 minutes in the process).

[13] Krzewina and his teammates qualified to the 4 × 400 metres relay final at the 2016 Summer Olympics in Rio de Janeiro, Brazil.

On the last straight, Krzewina overtook the anchor of the American team, which lead from the start, and achieved the greatest success in his career.