Bird-Smith began to take part in senior competitions towards the end of 2011 and on his international circuit debut at the Gran Premio Cantones de La Coruña, ending the race in 13th place. His debut in the 20 kilometres race walk event came in December and he recorded a time of 1:26:38 hours. He bettered this on the 2012 IAAF World Race Walking Challenge circuit, setting a time of 1:23:15 hours in Taicang. He ranked 43rd in the senior 20 km race at the 2012 IAAF World Race Walking Cup before winning his first national title in August.[7]
A second national title came at the 2013 Australian Athletics Championships, this time in the 5000 m walk – an event in which he also set a best of 18:56.96 minutes to rank third in the world that year. He set a personal best at the Oceanian Championships 20 km race, taking second behind his compatriot Jared Tallent and had his first top three finish on the circuit at the Coppa Città di Sesto San Giovanni. A new best of 1:22:03 following at the La Coruña race, where he was fourth overall.[7] This built up to his debut appearance for Australia the 2013 World Championships in Athletics, at which he performed well with an eleventh-place finish, marking his entry into the top tiers of international competition, and also outdoing his father's highest placing at the event.[5] He ended 2013 by defending his 20 km national title.[7] In 2016 Dane won a bronze medal in the 2016 Rio olympics.
Bird-Smith made some quick improvements in the 20 km event in 2014. After winning his first Oceanian title in February,[8] he walked 1:21:01 for third in Nomi, Ishikawa,[7] then achieved a lifetime best of 1:20:27 hours at the 2014 IAAF World Race Walking Cup, ranking 14th.[9] With no other major championships to compete at, he took to the circuit and won the British Grand Prix of Race Walking as well as a third straight Australian 20 km title.[10] He ranked in the global top-25 for the year.[11]
In 2015, Bird-Smith placed fifth at both the IAAF Race Walking Challenge Taicang and La Coruña race, setting a new best of 1:20:05 hours at the latter.[12] This preceded his first ever global gold medal, which the University of Queensland student achieved at the 2015 Universiade, narrowly overturning the lead of Canada's Benjamin Thorne.[13]