New South Wales Liberal Senator and former Howard minister Helen Coonan has confirmed she is retiring after 15 years in federal politics.

Senator Coonan has told the Upper House she has decided to retire on Monday even though her term does not expire for another three years.

In her farewell speech, she said it was the end of an era because she was the last person to have been a Minister in the Howard Government still in the Senate.

Senator Coonan was swept into government along with the John Howard in 1996 and was re-elected in 2001.

She was appointed minister for revenue and assistant treasurer in 2001, making her the first woman to hold an Australian Treasury portfolio.

In 2004, Senator Coonan was appointed Minister for Communications, Information Technology and the Arts, which she held until the 2007 election defeat.

She also used her farewell speech to warn about the growth of coal seam gas mining.

"Many Australians have become uneasy about whether such investment for mining purposes, most particularly coal seam gas licences, will affect prime agricultural land," she said.

"[They] question the impact this might have on Australia's land use and future food security."

Senator Coonan told the ABC the current boom in coal seam gas mining requires a better system to balance the rights of farmers and mining companies.

"What I'm particularly interested in is looking at perhaps an opportunity to identify what is prime agricultural land, to see whether it's feasible to quarantine that land, and to then develop a system where there can be responsible multi-use of that land," she said.

"I just think that perhaps the balance needs to be looked at."

'Alliances shift'

Senator Coonan says she believes her political swing has remained unchanged since entering office.

"You are what you are and you do form alliances from time to time. So while I don't think I've changed at all, I'm fairly much a centrist," she said.

"Certainly alliances around you shift. And in the Liberal Party alliances tend to shift a bit on issues; it's not as factional as the Labor Party appears to be."

During her time in the Senate Senator Coonan banded together with other women to stop now-Opposition Leader Tony Abbott's push on a number of woman's issues, including the legality of abortion drug RU486 and whether Medicare funding should go to IVF treatment.

However she says she does not view Mr Abbott's rise with any trepidation.

"Having worked with him through these issues, I found him to be responsive when the views of women were actually able to be articulated, certainly by his senior cabinet colleagues," she said.

"My position has always been, and I have absolutely no problem in saying it, that I don't think that the Government has a role to second-guess women's choices.

"I don't think that the Government has any role sitting looking over any woman's shoulder.

"I think that the obligation of government is to make those particular services that women need available and safe and then it's time to go out of somebody's life."

Senator Coonan says she is absolutely confident Mr Abbott is across issues that are of concern for woman.

"I would have every confidence that Tony is well and truly across the things that matter very much to women," she said.

Successor

Arthur Sinodinos is being lined up as a possible successor to Senator Coonan.

Many Liberals want Mr Howard's former chief of staff, Arthur Sinodinos, lined up as a successor to take over the vacant Senate seat, and Senator Coonan says she will leave it up to the party, but he would make a good addition.

"If Arthur commits, and I think there's still an issue as to whether he is prepared to do the things that are necessary to take up this wonderful opportunity and get the selection, he would be a very, very able addition to our team."

Senator Coonan says she spoke to Mr Sinodinos and suggested he would find the Senate as wonderful as she had.

She says the Coalition was able to pass a number of difficult pieces of legislation through the Senate while it enjoyed a clear majority in both houses.

"Having the majority in the Senate enabled me to get through some very difficult things that had been in the too-hard basket," she said.

"I do think that the Senate is a very important institutional safeguard on the workings of democracy, excesses of executives; that's always been the theory and I think that's how it works in practice."