 Marx was first selected for the Springboks for the 2016 Rugby Championship, making three appearances for his country during 2016.Marx made his debut for the Springboks on 17 September 2016, the same date as team mate Francois Louw's 50th test.Marx replaced Springbok captain Adriaan Strauss in the 43rd minute, but had a disappointing debut, with South Africa losing to New Zealand 13-41.