He played at club level for the Cronulla-Sutherland Sharks, the South Sydney Rabbitohs, the St George Illawarra Dragons, and the Melbourne Storm, in the National Rugby League (NRL), as a prop or second-row.

[6] Following his retirement from rugby, Greenfield became a prominent figure within the Construction, Forestry, Maritime, Mining and Energy Union (CFMEU) NSW branch, holding the position of assistant secretary.

[8] He was arrested earlier that year along with two union organisers Nicholas Rekes and Simon Gutierrez during a police operation targeting drug distribution in Sydney’s eastern suburbs.

[16] December 2024 it was announced that the investigator for the CFMEU administration, Geoffrey Watson, SC, is looking into $30,000 a month in so far unaccounted payments that the NSW branch transferred directly to the accounts of former secretary and assistant secretary Darren and Michael Greenfield from 2021 to 2023. he payments were discovered as part of a broader investigation into union board resolutions to pay the Greenfields’ “reasonable legal expenses” in defending criminal charges over alleged corruption.

In a letter sent to former members of the CFMEU branch committee of management (BCOM) this month, seen by The Australian Financial Review, Mr Watson said he was investigating the circumstances behind the $3.15 million payment, who approved it, and its purpose.

[17] In December 2024 , father and son Darren and Michael Greenfield were successful in delaying the upcoming fraud charges case due to the High Court challenge regarding the administration of the CFMEU as to who was going to fund their defense team - themselves or use members monies.

The Commonwealth lawyer did not oppose this and they have been granted a stay until February 18 2025[18] As reported in the national papers in February 2025 Mark Irving KC the CFMEU administrator received a report from Geoffrey Watson SC recommending that Darren and Michael Greenfield face criminal charges for dishonestly using positions to gain financial advantage in relation to the transfer of $3.15 million dollars of members money to fight bribery charges.

The report also recommends that Rita Mallia and Rob Kera also face civil proceedings for failing to consider the reasonable expenses they approved for facilitating the $3 million dollar payment.