Barangaroo workers ceased their duties this morning, putting construction on hold and a counsellor on hand.
The union is raising money for the 23-year-old man's family, and Lend Lease say they will match the total amount raised dollar for dollar.
The young worker had completed his Koori Job Ready program in December 2013.
Following his graduation, he secured a job working in the construction industry, most recently on the Barangaroo development site in Sydney.
In a statement, program organisers said, "the loss has had a profound effect within our community, and our support and thoughts are with his family during this difficult time."
Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14, or MensLine Australia on 1300 78 99 78.
