The remarks were made in an email to former Waitangi Tribunal director Buddy Mikaere after being criticised for skipping off to Paris with his wife while on a parliamentary trip to Europe.
Mr Harawira has called the press conference for 3pm today and is expected to speak publicly on his emailed comments, which included referring to "white motherf...ers".
Mr Harawira will first appear on a Radio Live programme hosted by Maori commentators Willie Jackson and John Tamihere, due to go on air about 1pm.
TV3 News reported last night a Maori Party hui arranged for Thursday to discuss how Mr Harawira could atone for his comments had been brought forward to today.
Mr Harawira was part of a parliamentary delegation visiting Europe when he decided to leave Brussels and take his wife to Paris for the day.
He was unrepentant about that, saying he paid for the trip himself, but he is reported to have misled Maori Party co-leader Tariana Turia over it.
Subsequently, Mr Mikaere sent Mr Harawira an email questioning the Paris trip.
In response, Mr Harawira sent an email saying: "Gee Buddy, do you believe that white man's bullshit too? White motherf...ers have been raping our lands and ripping us off for centuries and all of a sudden you want me to play along with their puritanical bullshit."
Prime Minister John Key yesterday said Mr Harawira should apologise for his response to Mr Mikaere's email.
"I definitely think he owes a bit of an apology," Mr Key said.
"It's for the Maori Party leadership to sort that out, and I have got to say they are doing their best to try and deal with that situation."
Mr Key said there was "a tinge of racism in those comments".
"He's a shock jock kind of MP... the problem is he says things and does things that are a bit outrageous."
Maori Party leaders decided yesterday he wouldn't be expelled from the party but they appeared to at least expect a public apology.
"I think he will find a way to apologise to the nation," party president Whatarangi Winiata said on Sunday.
"We will help him do that."
However, party co-leader Pita Sharples said yesterday he wouldn't order an apology.
"An apology is something from the heart and the mind and I'm not going to tell someone they have to apologise," he said.
"I can say it's my wish that they would but you can't order someone to apologise."
Race Relations Commissioner Joris de Bres also called for an apology, and suggested yesterday that Mr Harawira deliver that in Parliament.
The commission received more than 20 complaints about the email but said yesterday Mr Harawira's language did not breach to Human Rights Act.
