In a statement today, he said: “It was my decision to resign; and my decision alone. I was not pushed by anyone.”
“However I did feel some of my colleagues may have been aggrieved that the enforcer of discipline was being somewhat ill-disciplined himself,” he added.
The maverick MP said Nationals leader Barnaby Joyce had been incredibly supportive and would have supported whatever decision was made.
“I thank him and the rest of the Nationals team for the great honour of serving as their Chief Whip over the last six months,” Christensen said.
His decision comes just a day after an opinion poll revealed he is staring down a challenge from Pauline Hanson's party in his seat of Dawson ahead of the 2019 election.
Just last week the outspoken backbencher pledged his support to the National Party after urgent peace talks with leader Barnaby Joyce.
"I'm loyal to Barnaby Joyce, I'm loyal to the National Party, loyal to the LNP," Mr Christensen said at the time.
Mr Joyce travelled north to persuade Mr Christensen not to leave the party and to ease tensions over a dispute which could see jobs lost in the sugar cane industry.
It will take effect from Thursday when Nationals MPs and senators will meet to elect a replacement.
Mr Christensen said his position had become untenable after speaking out on several issues in recent months.
