[14] On 8 June 2016, Ludwig signed a two-year contract with Danish Superliga club AC Horsens, after their head coach Bo Henriksen had referred to him as his "dream player".
[15][16] He made his debut on 14 July, playing the full match in a 2–1 away win over rivals AGF, marking his return to Danish top-tier football since his sole appearance for Midtjylland in 2011.
[17] Ludwig would have a strong season in the centre of defense alongside Bubacarr Sanneh,[18] helping an overperforming Horsens-team reach the championship round where they eventually ended sixth in the league table.
[25][24] He made his return to the pitch for Horsens on 19 August, five days after signing, in a 2–0 away loss to AGF on Aarhus Stadium, where he started in the centre of defense next to Malte Kiilerich.
[26] On 3 June 2020, Ludwig was voted into the "Team of the Week" of the Danish Superliga, after stringing together some strong performances in a rejuvenated Horsens-defense, beating league leader FC Midtjylland 1–0.