On 15 April 2017, at a Newcastle Pro Wrestling event, Farrelly made his debut under the ring name Matty Wahlberg, losing to SnapChad.

[4] Wahlberg would form a tag team with Carter Dreams, known as The BABES (Blonde And Blue Eyed Squad), managed by Harley Wonderland.

[5] At the PWA Black Label: Break Their Back & Make Them Rumble event, Wahlberg lost to TJ Perkins.

[9] On the 11 June episode of 205 Live, he made his WWE debut under the ring name Grayson Waller, defeating Sunil Singh.

On the 9 November episode of NXT, he lost to Solo Sikoa in a triple threat match which also included LA Knight.

[13] On the following episode of NXT, Waller brutally attacked Johnny Gargano during his farewell promo where he thanked his fans and friends, thus cementing his heel turn.

[18] At NXT: Roadblock on 8 March, Waller defeated Knight in a Last Man Standing match when he used Sanga to make it to his feet and beat the ten count.

[24] Waller would then pursue the NXT North American Championship by tricking Carmelo Hayes into signing the contract.

At NXT: The Great American Bash on 5 July, Waller lost to Hayes due to interference from Trick Williams and Wes Lee.

[25] Despite this, Waller blamed his loss on Wes Lee and defeated him on the 26 July episode of NXT due to interference from Williams.

[41] On the 15 December episode of SmackDown, both Waller and Theory lost in the first rounds of the United States Championship #1 Contender Tournament to former rival Carmelo Hayes and Owens respectively.

(Karl Anderson and Luke Gallows) on the 22 March episode of SmackDown and The Street Profits (Angelo Dawkins and Montez Ford) in the finals one week later to qualify for the six-pack ladder match for the Undisputed WWE Tag Team Championship at WrestleMania XL.

[46] On the May 3 episode of SmackDown, Theory and Waller defeated The Street Profits (Angelo Dawkins and Montez Ford) in their first title defense.

[47] On the July 5 episode of SmackDown, Grayson Waller and Austin Theory as A-Town Down Under lost the titles to #DIY (Johnny Gargano and Tommaso Ciampa), ending their reign at 90 days.

He competed on the Contenders team, and garnered attention for his outspoken personality, essentially playing a version of his Matty Wahlberg wrestling character on reality television.

[63] Farrelly is a supporter of the NRL's Sydney Roosters, the NFL’s Philadelphia Eagles, and the NBA's Sacramento Kings.