Just like his twin brother, Kevin Borlée obtained his first senior title at the age of 18: the Belgian Indoor championships in 2006 in Ghent, where he won the 400 m, while his brother won the 200 m. Later on, Borlée would add 3 more Belgian indoor titles: once more on the 400 m and two on the 200 m. On 31 May 2008 Kevin and Jonathan took part in the 4 × 400 m on a meeting in Neerpelt.

On the 4 × 400 m relay, with teammates Jonathan Borlée, Cédric Van Branteghem and Arnaud Ghislain, they qualified for the final with a new national record of 3:00.67s.

[2] At the end of 2008, Kevin Borlée moved together with his brother Jonathan to Tallahassee to enroll in Florida State University.

Directly after the World Championships, it became clear that Kevin Borlée had sustained the same injury that ruled out his brother Jonathan 6 weeks earlier: a stress fracture on the tarsus.

The story shows many similarities with the stress fracture of the tibia of the Swedish hurdles sprinters Susanna and Jenny Kallur.

In the final, Borlée seemed to fall back after a good start, but with an impressive sprint in the last 50 m, he passed the pack to win in front of Britain's Michael Bingham and Martyn Rooney in 45.08s, a season's best.

The Belgian 4 × 400 m relay team, which besides Kevin Borlée included Antoine Gillet, Cédric Van Branteghem and Nils Duerinck, reached the final.

[1] The Belgian 4 x 400 team that Borlée was in set a new area record in winning the gold medal of the European Indoor Championship.

At the 400 m of the European Championships in Berlin, Kevin Borlée reached the final with a win in heat 1 in 45.29s and a 3rd place finish in the 3rd semi-final in 45.07s (fastest losing time) .

In the final, Borlée had his trade mark slow start, but with an impressive sprint in the last 100 m, he passed the pack to come in second after Britain's Matthew Hudson-Smith in 45.13s.

The Belgian 4 × 400 m relay team, which included Julien Watrin, Robin Vanderbemden, 2018 junior world champion Jonathan Sacoor and younger brother Dylan, reached the final with a win in heat 2 in 3:02.44s, the 4th fastest qualifying time.

The progenitor of the Borlee family is Jacques, bronze medalist at the 1983 European Indoor Championships in Budapest on 200 m, while his first wife Edith Demaertelaere was a good sprinter with a personal best of 23.89.

The four sons are all 400 m specialists, the twins Jonathan and Kevin, both Olympic finalists in London 2012, Dylan and the youngest Rayane.