Lowndes made his debut on the inter-county scene when he was selected for the Dublin minor teams as a dual player in 2011. After back-to-back All-Ireland defeats with the hurlers, he ended his minor career as an All-Ireland medal winner with the footballers in 2012. He subsequently joined the Dublin under-21 team and won an All-Ireland medal in this grade in 2014. Lowndes made his senior debut during the 2014 league. Since then he has won three successive All-Ireland medals. Lowndes has also won four Leinster medals and three National League medals.