Tearney made his ATP main draw debut at the 2015 Heineken Open, where he received a wildcard into the doubles competition, partnering Wesley Whitehouse.

He made his ATP singles main draw debut at the 2016 ASB Classic.

[1] Winning the New Zealand championships gained Tearney a wild card entry into the qualifying draw for the 2019 ASB Classic, where he lost in the first round to Thomas Fabbiano.

A few weeks later he was in Portugal where, in an epic match with more than a dozen rallies of twenty shots or more, he beat Jacob Grills in the final of the ITF Futures tournament in Vale do Lobo.

Tearney was called up to the New Zealand Davis Cup team in March 2020 for their tie against Venezuela, despite no longer playing tennis professionally and working for a property development company, and defeated Jordi Muñoz Abreu in the first singles rubber in straight sets 6–4 6–4.