In the semifinal match Daniell and Tecău faced Johan Brunström and Jean-Julien Rojer who had defeated grand slam winners Lukáš Dlouhý and Leander Paes.
He achieved his best win when, having had to qualify for the 2017 Swiss Indoors in Basel because Demoliner was playing in Vienna, he and new partner Dominic Inglot beat the top seeds, the world's second-ranked pair of Henri Kontinen and John Peers, in the first round.
They drew third seeds and eventual semi-finalists Ekaterina Makarova and Bruno Soares as their first-round opponents and, although winning the second set, were outclassed in the match tie-break, the final score being 6–3, 5–7, 10–2.
Daniell and Artem Sitak teamed up for the doubles in the Davis Cup tie against China, but were beaten by Gong Mao-Xin and Zhang Ze.
In that match Daniell aggravated an injury to his right wrist which he had picked up during the Davis Cup tie against China, and announced later that he would miss the rest of the clay court season to concentrate on his rehabilitation.
He and Koolhof lost in qualifying, but became lucky losers and beat the wildcard combination of Novak Djokovic and Stan Wawrinka in the first round, before going down to Jamie Murray and Bruno Soares in a match tie-break.
Scheduled to play the doubles rubber with Artem Sitak, Daniell had to withdraw on the morning of the match due to a recurrence of a back injury, his place being taken by Ajeet Rai.
They were the only seeded team to reach the semi-finals, where they beat Julien Benneteau and Lucas Pouille, and they met the British pair of Luke Bambridge and Jonny O'Mara in the final.
Daniell and Koolhof began their year in Brisbane, needing tie-breaks of one kind or another in all three matches on their way to the final, where they defeated fourth seeds Rajeev Ram and Joe Salisbury in straight sets, 6–4, 7–6 (6).
In the Australian Open they beat the wildly popular home pair of Lleyton Hewitt and John-Patrick Smith in three sets, before falling to Michael Venus and Raven Klaasen in the second round.
In a career-best performance for the New Zealander at a Grand Slam event, Daniell and Koolhof got to the quarter-finals at Wimbledon, where they were beaten in straight sets by Ivan Dodig and Filip Polášek.
In another career-best effort, Daniell and Jennifer Brady made the third round of the mixed doubles before losing to eventual semi-finalists Matwé Middelkoop and Yang Zhaoxuan.
Daniell also played mixed doubles at the US Open, partnering Croatia's Darija Jurak, but they were well-beaten in the first round by the second seeds, Gabriela Dabrowski and Mate Pavić.
In September he and Michael Venus won the doubles rubber in New Zealand's Davis Cup tie against Indonesia, before Daniell linked up with what he hoped would be his new long-term partner, Philipp Oswald.
They then lost in the first round four times in a row, at the Australian Open to sixth seeds Marcel Granollers and Horacio Zeballos, in New York and Delray Beach to Marcelo Arevalo and Jonny O'Mara and, in somewhat of an upset, to Grigor Dimitrov and Taylor Fritz in Acapulco.
Daniell resumed his career in the US Open at the beginning of September, where he and Oswald defeated Raven Klaasen and Oliver Marach in the first round, but were upset by the American wild card pair of Christopher Eubanks and Mackenzie McDonald in the second.
Daniell and Oswald then moved on to Cologne, where they lost to French Open champions Kevin Krawietz and Andreas Mies in the semi-finals, and followed that with a quarter-final loss in Nur-Sultan.
Their final tournament for the year was the Paris Masters, where they beat Krawietz and Alexander Zverev in the first round before losing to Jürgen Melzer and Édouard Roger-Vasselin.
[15] In December 2023, after a long injury break, he resumed his career by finishing runner-up in the non-tour Wellington Open, and then won the ITF M15 event at the same venue a week later, both times with Finn Reynolds as his partner.