[4] Moses played his junior football for the Holy Cross Rhinos and Carlingford Cougars[5] before being signed by the Parramatta Eels.

Moses played for the Eels' Harold Matthews Cup team before being signed by the Wests Tigers.

A late selection at halfback after Luke Brooks withdrew, Moses contributed to four tries in the victory, and was said to have, "directed the team superbly," as they won 30-8.

Moses had been slated to make his NRL debut the next weekend, but was unable to be selected due to his suspension.

It was noted that his first year was "a tough start to life in first-grade for the local junior, particularly as the club imploded on and off the field".

[21] With the absence of Robbie Farah and Luke Brooks, Moses was the Tigers' key playmaker for the season opener in Round 1 against the New Zealand Warriors.

After Robbie Farah was dropped to reserve grade towards the end of the year, it was said, "A large reason for the Tigers' success over the past six weeks has been the form of five-eighth Mitchell Moses, who has been the club's best player over that period.

"[23] Phil Gould named him as his five-eighth of the year, saying, "His back half of the season has been as good as any player in the game and he only appears to be getting better.

[25] On 24 September, Moses made his representative debut with the Prime Minister's XIII against Papua New Guinea, scoring 3 tries and kicking 4 goals in the 58-0 thrashing win in Port Moresby.

[27] Early in the season, Moses, alongside Tigers captain Aaron Woods, halves partner Luke Brooks and fullback James Tedesco, attracted media attention as their contracts all expired at the end of the year.

Moses played at halfback in the Eels losses to the Melbourne Storm and North Queensland Cowboys as they stumbled out of the finals, the first top 4 team since Manly in 2014 to go out in straight defeats.

With seven minutes remaining in the match against Cronulla, Parramatta were losing 22-4 when they scored three late tries to make it 22-20 on the full time siren with Moses getting the last try.

It was initially thought that he had suffered a posterior cruciate ligament injury but scans showed no major damage was done and instead he would miss 2-3 matches.

[44] On 19 July, Moses scored the match-winning try in Parramatta's 14-8 victory over arch rivals Canterbury, which the media dubbed the "spoon bowl" as the teams were sitting second last and last on the ladder.

In Round 6, Moses was the first player to score a try, conversion and field goal in the first NRL match played at the new Bankwest Stadium in which Parramatta defeated Wests Tigers 51-6.

The first try to be officially scored at the new stadium was by teammate Bevan French who crossed for the Wentworthville Magpies against Western Suburbs in the Canterbury Cup NSW match played before the main game.

[50][51][52] On June 8, Moses signed a three-year deal worth $2.5 million, keeping him at the club until the end of the 2022 season.

In the elimination final against Brisbane, Moses scored 2 tries and kicked 6 goals as Parramatta won the match 58-0 at the new Western Sydney Stadium.

It was the first time Moses had represented NSW and his selection came off the back of an injury to Penrith halfback Nathan Cleary in the second game of the series.

[63][64] On 20 July, it was announced that Moses would be ruled out from playing for an indefinite period after sustaining a back fracture in game 3 of the 2021 State of Origin series.

[65] Moses played a total of 22 games for Parramatta in the 2021 NRL season including both of the club's finals matches against Newcastle and Penrith.

[66][67] In round 4 of the 2022 NRL season, Moses scored two tries and kicked eight goals in a man of the match performance as Parramatta defeated St. George 48-14.

[71] In the 2022 Qualifying Final, Moses was taken from the field in the second half after suffering a head clash in Parramatta's 27-8 loss to Penrith.

[72] The following week in the elimination semi-final, Moses starred for Parramatta scoring a try and kicking six goals in a 40-4 victory over Canberra.

[79] On 12 June, Moses was selected by New South Wales to play in game 2 of the 2023 State of Origin series after Nathan Cleary was ruled out due to an injury.

[80] Moses was retained for game 3 in which New South Wales defeated Queensland to avoid a series clean sweep.

In round 20, Moses kicked a field goal with less than five minutes remaining to win the game for Parramatta 25-24 over the Gold Coast.

[84][85] Despite showing indifferent form since his return to the Parramatta side, Moses was selected by New South Wales for game two in the 2024 State of Origin series.