Nicholls started training in Perth at the Dynamite Factory, the wrestling school of Explosive Pro Wrestling. He moved to California and started working for promotions in the United States, such as Pro Wrestling Guerrilla, NWA Pro, and World League Wrestling.
Nicholls has trained at the New Japan Pro Wrestling's L.A. Dojo, based in Los Angeles. He wrestled for NJPW in Tokyo in 2006. Also in 2006, Nicholls unsuccessfully challenged for the NWA British Commonwealth Heavyweight Championship.
In June 2007, after NWA split with TNA, Nicholls was involved in the Reclaiming the Glory tournament to crown a new NWA Heavyweight Champion, but was defeated in the tournament by Fergal Devitt. In September 2007, Nicholls defeated champion Karl Anderson and Ryan Taylor in a 30-minute Iron Man match for the Empire Wrestling Federation American Championship. In 2009, Nicholls wrestled for Ring of Honor.
On 23 February 2011 Haste made his debut in Pro Wrestling Noah as he had a try-out match against his teammate Shane Haste. A month after the try-out match both men started to work full-time with the Japanese promotion. Nicholls competed in both the 2012 and 2013 Global League tournaments as a singles competitor. On 7 July 2013 Haste and Nicholls, known together as The Mighty Don't Kneel (TMDK), won the GHC Tag Team Championship after they defeated Toru Yano and Takashi Iizuka. On 16 September, Nicholls unsuccessfully challenged Kenta for Noah's top title, the GHC Heavyweight Championship. At the end of 2013, the Tokyo Sports magazine named Nicholls and Haste the tag team of the year, making them the first foreign team to win the award since Stan Hansen and Vader in 1998. Nicholls and Haste lost the GHC Tag Team Championship to Maybach Taniguchi and Takeshi Morishima on 25 January 2014. They regained the title from Dangan Yankies (Masato Tanaka and Takashi Sugiura) on 10 January 2015. They lost the title to K.E.S. (Davey Boy Smith Jr., Lance Archer) on 11 February. On 28 December 2015, Noah announced that Nicholls and Haste would leave the promotion following their contracts expiring at the end of the year. On 11 February 2016, Noah announced that Nicholls and Haste would return to the promotion the following month to take part in a five-show-long farewell tour, entitled "Departure to the World". Their final Noah match took place on 10 March and saw them defeat Naomichi Marufuji and Mitsuhiro Kitamiya.
After starting out in Noah, Nicholls returned to the United States and Ring of Honor in February 2012. He and Haste won a tournament at ROH Rise & Prove, defeating two other teams to qualify for a match against the Briscoe Brothers. At the ROH Showdown in the Sun iPPV in March 2012, the Briscoe Brothers defeated Nicholls and Haste in a Proving Ground match.
Also in February 2012, Nicholls and Haste wrestled television matches for NWA Championship Wrestling from Hollywood. Also in March 2012, Nicholls and Haste started wrestling for Ohio Valley Wrestling, during their stint there, they were defeated in a title match for the OVW Southern Tag Team Championship by Rudy Switchblade and Jessie Godderz.
On 20 December 2014, Nicholls and Haste made their debut for New Japan Pro Wrestling, when they, along with Naomichi Marufuji, were revealed as Toru Yano's tag team partners at Wrestle Kingdom 9 in Tokyo Dome on 4 January 2015. At the event, the four defeated Suzuki-gun (Davey Boy Smith Jr., Lance Archer, Shelton X Benjamin and Takashi Iizuka) in an eight-man tag team match.
In June 2015, Nicholls and Haste took part in a WWE tryout camp. In February 2016, it was reported that Nicholls and Haste were scheduled to join WWE's NXT brand following their Noah farewell tour.
On 25 March 2016, WWE confirmed the signings of both Nicholls and his tag team partner, Shane Haste. They began training at the WWE Performance Center in April, while working for the promotion's developmental branch NXT. During the May 19 NXT tapings, Nicholls and Haste were renamed Nick Miller and Shane Thorne, respectively, while TMDK was renamed TM61. They debuted on the May 25 episode, losing to Johnny Gargano and Tommaso Ciampa.
Miller will be making his WWE video game debut as a playable character in WWE 2K18.Finishing moves
Blue Vengeance (Moonsault)
Mikey Bomb (Spin-out powerbomb)
Shooting star press
Southern Cross Stretch (Modified figure-four leglock)
Forearm smash, sometimes sliding
"Joker & the Thief" by Wolfmother
"Stand Tall" by CFO$
Empire Wrestling Federation
EWF American Heavyweight Championship (1 time)
Explosive Professional Wrestling
EPW Championship (2 time)
EPW Tag Team Championship (2 times) – with Shane Haste
EPW Wrestler of the Year (2004, 2005)
EPW Best Wrestler of the first five Years (2006)
EPW Match of the Year (2002) vs. Jimmy Payne at Retribution
EPW Telethon Rumble winner (2009)
NWA Pro Wrestling
NWA Australian National Heavyweight Championship (1 time)
NWA Australian National Championship Tournament winner (2007)
Pro Wrestling Illustrated
PWI ranked him #154 of the top 500 singles wrestlers in the PWI 500 in 2016
Pro Wrestling Noah
GHC Tag Team Championship (2 times) – with Shane Haste
Global Tag League Fighting Spirit Award (2015) – with Shane Haste
Ring of Honor
Rise and Prove Tournament (2012) – with Shane Haste
Best Tag Team Award (2013) – with Shane Haste
Westside Pro Wrestling
EPW Match of the Year (2012) TMDK vs. Team Victoria at State of Origin
International Impact Award (2009, 2011 co-winner)
Tag Team of the Year (2010) – with Shane Haste
The Grand Slam Club (2011)