Letschert began his football career with his hometown club, SDOB, before joining Ajax' youth academy at a young age.

Born in Purmerend, Letschert lived in Broek in Waterland in his early years and started playing football at the local club SDOB.

[10] After his disciplinary suspension, the centre-back played two more games in the first team of Groningen and on 30 January 2014, both sides came to the decision to terminate the contract by mutual consent.

Away against NAC Breda – a game which was lost 2–0 – Letschert was in the starting line-up under head coach Jon Dahl Tomasson.

At the end of August, a conflict arose between Roda JC on the one hand and Letschert and his agent Dick van Burik on the other.

[16] The Royal Dutch Football Association (KNVB) stated that the contract was valid and that club's willing to sign Letschert had to submit a transfer fee to secure his services.

Coach Rob Alflen let Letschert come on as a substitute twelve minutes before the end of the game to replace captain Mark van der Maarel.

[23] In the 2015–16 season, Letschert remained a regular starter and he often formed a duo at the center of the defense with Ramon Leeuwin or Van der Maarel.

At home, he secured a 2–0 win in injury time on a pass from Sébastien Haller against his former club Groningen, after Bart Ramselaar had opened the score.

There, he beat PEC Zwolle, but Heracles Almelo then proved too strong and qualified for the UEFA Europa League.

[25] On 3 August 2016, it was announced that Letschert had signed a four-year contract with Italian Serie A club Sassuolo for a deal worth €4 million.

That day, he came in for Domenico Berardi in the 72nd minute during a match against Red Star Belgrade in the final qualifying round of the UEFA Europa League.

[34][35] By then, Rick van Drongelen and Gideon Jung had established themselves as a partnership in central defense under head coach Dieter Hecking.

Letschert made his first brief appearance on 28 September in a 2–2 draw away against SSV Jahn Regensburg, coming on as a substitute in the 79th minute for Jung.

Prior to the final matchday, Letschert suffered an inner ligament strain in his knee during practice, which ended the season for him.

Finishing in fourth place of the league table, HSV missed promotion to the Bundesliga for a second consecutive year, whereupon his expiring contract was not extended.

[39] He made his debut for the club on 19 September in a match against PEC Zwolle, starting in central defense alongside Pantelis Chatzidiakos in a 1–1 home draw.

After two defensive errors in an away game against Twente on 23 September 2021, and as a result being substituted by head coach Pascal Jansen,[42] Letschert left the stadium on his own.

[45] On 3 October 2022, Letschert joined newly promoted Danish Superliga club Lyngby Boldklub on a deal for the rest of 2022.

[46] He made his debut for the club on 14 October, coming on as a substitute in the 74th minute for Pascal Gregor in a 2–0 loss at home against AaB.

[50] He made his debut for the club on 25 February, the first matchday of the season, starting in a 1–0 away victory against the Suwon Samsung Bluewings.