In May 2014, De Allende was one of eight uncapped players that were called up to a Springbok training camp prior to the 2014 mid-year rugby union tests. He was subsequently named in the final squad, but suffered a medial knee ligament injury and had to withdraw from the squad.
However, he was once again selected in the Springboks' next squad for the 2014 Rugby Championship and was named in the starting line-up for their opening match of this competition against Argentina in Pretoria.
In 2015, he was selected in the starting XV of a South African side against the World XV for a game held on 11 July 2015. He scored two tries in the game, earning praise from the World XV and former Australia coach Robbie Deans, who commented that "Damian has been playing remarkable rugby the whole year and he keeps doing the right things. He can add a new dimension to the Boks".
Having only been on the field for 13 minutes, De Allende was controversially red-carded in the 75th minute of New Zealand's 25-24 win against South Africa on 8 October 2017 for a late hit on first-five Lima Sopoaga, intending to charge down Sopoaga's attempted drop goal. De Allende was not suspended, as SANZAAR stated he should not have received red for the attempted charge down.
De Allende was named in South Africa's squad for the 2019 Rugby World Cup. South Africa went on to win the tournament, defeating England in the final. De Allende started in all three tests for South Africa during the 2021 British & Irish Lions tour to South Africa, earning his 50th cap for the Springboks during their third test victory that sealed a series win for the home team, and garnering widespread praise for his performances during the series.
De Allende won his second Rugby World Cup with the Springboks in 2023.
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