Scott Morrison does not have a majority in parliament but can officially count on independent Bob Katter's support to make sure he can keep governing.
The prime minister on Thursday signed a deal with Mr Katter, locking in the Queensland MP's vote on issues of confidence and supply.
In return, the government will fund up to $180 million for the Hughenden irrigation scheme and $54 million for the Hells Gate Dam.
"The agreement will support the continued stability of the government and us getting on with the job," Mr Morrison said in a statement on Thursday.
"It will protect against political disruption by the opposition."
The coalition lost its majority when independent Kerryn Phelps won Malcolm Turnbull's old seat of Wentworth, leaving Mr Morrison vulnerable to votes of no confidence.
"I agree to the proposals as outlined in this letter with appreciation," Mr Katter wrote.
Mr Katter is an irregular attendee at parliament during sitting weeks.
