As a junior, Duckworth enjoyed a successful career which included winning three titles and reaching the semifinals of the 2010 French Open.

Duckworth's first big result came in December 2007 when he made his first final in Manila, Philippines but had to retire in the third set against Francis Casey Alcantara.

Duckworth's first title came in August 2010 at the Oceania Closed Championship held in Fiji, he beat fellow Australian Maverick Banes in the final.

Out of the nine junior tournaments Duckworth entered in 2010 he managed to reach three finals that resulted in two titles won in Kuching, Malaysia and Manila, Philippines respectively.

Duckworth entered his first professional tournament in September 2006 as a 14-year-old in Happy Valley, South Australia where he was defeated in the first round of qualifying.

He entered his second pro tournament in September 2007; the event was held in Sawtell, New South Wales, and Duckworth made it to the final round of qualifying, but fell at the last hurdle.

In November 2008, Duckworth received a wildcard into a Futures tournament held in Perth and made the most of his opportunity; he recorded his first main draw victory in the first round.

The following week, Duckworth received another wildcard into an event held in Sorrento, Western Australia, but could not keep the form going as he fell in the first round to James Lemke.

[3] The 2010 season began for Duckworth with a qualifying wildcard into his hometown ATP event in Sydney where he lost in the first round to fellow Australian Marinko Matosevic 1–6, 3–6.

Duckworth began the year playing in the 2011 Brisbane International and the 2011 Australian Open qualifying tournaments after receiving wildcards into each event.

[1] His latest futures title was in Este Padova where he defeated Australian Jason Kubler en route to the final against Daniele Giorgini.

[4] Duckworth capped off the year by reaching the final of the 2012 Australian Open Men's Wildcard Playoff, falling to Marinko Matosevic 6–4, 6–1, 6–2.

in January 2012, in the first round of his first ATP main-draw event at the 2012 Brisbane International Duckworth drew Frenchman Nicolas Mahut.

On his Grand Slam debut at the 2012 Australian Open, Duckworth drew Estonian Jürgen Zopp in the first round and came out victorious in straight sets 6–3, 6–4, 6–4.

Duckworth then competed in the 2013 Nature's Way Sydney Tennis International losing to compatriot Samuel Groth in the quarterfinals 6–7(2), 6–7(5).

In July, Duckworth competed in the Lexington Challenger where he defeated countrymen Jordan Thompson in the second round and Thanasi Kokkinakis in the semifinal.

At Indian Wells, Duckworth qualified and defeated Dominic Thiem in round 1 before losing to Fernando Verdasco, as a result of his performance, he secured a top 100 ATP ranking for the first time in his career on 23 March 2015.

He then returned to the challenger tour playing in San Luis, Anning and Bordeaux where he lost in the semi-finals, quarter-finals and second round respectively.

He played a number of challenger events to finish the season making the quarter finals in Ho Chi Minh, Ningbo and Knoxville.

Duckworth was awarded a wild card into Sydney, where he defeated Íñigo Cervantes and lost to Jérémy Chardy in round 2.

In July, Duckworth qualified for the main draw at the 2016 Citi Open, losing in the second round to the top seed, John Isner.

In November, Duckworth won his second and third Challenger titles of the year, defeating compatriot and maiden finalist Marc Polmans in Canberra and Tatsuma Ito in Japan.

In February 2020, Duckworth reached his first ATP Tour semi-final in Pune, India, losing to Egor Gerasimov in straight sets.

Duckworth commenced the 2021 season at the 2021 Murray River Open where he defeated Ugo Humbert his first win over a top-50 opponent in more than four years.

In March, at the 2021 Miami Open he reached the third round of a Masters 1000 for the first time in his career defeating 8th seed David Goffin for his first top-20 win.

[28] In August, Duckworth qualified for the Canada Open and defeated world number 15 Jannik Sinner to reach the third round.

In September, Duckworth won the 2021 Amex-Istanbul Challenger II and achieved a career high singles ranking of World No.

He defeated 14th seed Roberto Bautista Agut, his third top-20 win for the season and in his career,[33] Lorenzo Musetti and fellow Australian Alexei Popyrin en route.

Although he reached the quarterfinals at the 2022 San Diego Open defeating compatriot Alexei Popyrin and Mitchell Krueger, he fell out of the top 100 on 26 September 2022 to No.

[36] He reached the quarterfinals of his home warm-up AO tournament at the 2024 Brisbane International as a qualifier and returned to the top 100 on 8 January 2024.