As we proceed through the last two sittings weeks before  June 30, those senators whose terms expire on that date are giving their valedictory speeches. Some, like Ron Boswell and Mark Bishop, who gave their speeches yesterday, are fixtures of the upper house and well known. Others have been on the red leather for a shorter period and their departure is unlikely to be as widely acknowledged.

In the case of Queensland LNP Senator Sue Boyce, who will deliver — likely with her usual dry wit — her valedictory this afternoon, that’s a shame. Indeed, it’s a shame she’s leaving the Senate, because Boyce, in her seven-year career in the Senate, has been an all too rare politician: thoughtful, brave, outspoken and prepared to stick to her principles.

That she replaced Santo Santoro, a man for whom, shall we say, those adjectives are perhaps a less obvious fit, is one of the small, lovely ironies that politics produces every now and then.

It was Boyce who crossed the floor in 2009, after former Liberal leader Malcolm Turnbull had been removed by a climate denialist putsch, to vote for the emissions trading scheme that he and Coalition MP Ian Macfarlane had negotiated with Labor MPs Kevin Rudd and Penny Wong. She rose, picked up her handbag and took the lonely walk across the Senate chamber to join Judith Troeth, another Senator of similar guts, on the then-government side.

Her speech that morning is worth reading in full, because even now it contains wisdom on climate action that this government is so flagrantly ignoring in its mindless destruction of a functioning carbon price.

“I become very concerned by people who use those sorts of false sciences to attempt to mislead Australian consumers into thinking that it is safe to continue to do what we are doing. As Senator Troeth pointed out, there are very few scientists in this place. But I think we should be using the science that is available to behave responsibly, not to encourage fear or scepticism that is wrong and unnecessary.”

And she brought to bear her own background as a successful businesswoman:

“My own background is as a manufacturer. In that sphere, I know the benefits of early adoption. I would just like to point out to the Senate that it was the Shergold taskforce, commissioned by the Howard government, who said, long before we got to this place, that Australia should not wait until a genuinely global agreement has been negotiated, because there are benefits which outweigh the costs in early adoption by Australia of an appropriate emissions constraint.”

Boyce wasn’t happy with the carbon pollution reduction scheme (a badly flawed Labor scheme further neutered in negotiations with Turnbull) — she preferred a straight carbon tax, she said, thereby echoing the strongly expressed view of her newly minted leader Tony Abbott just months earlier, when he’d called a carbon tax “the intelligent sceptic’s way of dealing with minimising emissions”.

But beyond that, and in answer to the internal critics who would rapidly swell in numbers in response to her decision, as far as Boyce was concerned, she was supporting her party’s policy:

“I realise that, by supporting the amended CPRS, I will disappoint many constituents within Queensland. I would like to say to them that I am acting in what I believe is good faith. I am supporting the party policy of less than 24 hours ago. When I rose to speak to say that we should accept the amended bill, I was supporting party policy. I find that I can do nothing else except continue to do that.”

Boyce crossed the floor a second time in June last year on same-sex marriage, this time taking the walk across the chamber by herself. She was less diplomatic this time around, though still made the point that the LNP allowed her the freedom to vote with her conscience.

“Surely in 2013 we are past the homophobic, scared-of-difference, scared-of-diversity view that would be implied by any sort of attempt to put into the Constitution the idea that marriage is between a man and a woman only. My only hope is that the appalling record of referenda in Australia — their complete lack of success — means that that would go down. But it would not go down just because we are not very good at passing referenda; it would go down because in 2013 it is a disgusting and immoral idea to want to take that point … I do not know what we can do, other than something like this, to try to persuade others that same-sex marriage is not going to be the end of the world for anybody, especially not for children or couples in Australia.”

Boyce’s strongest championship, however, was on disability and on women in Parliament. She was a strong supporter of a national disability insurance scheme from the moment the Productivity Commission recommended one; she urged an interim package of support for carers and the disabled while the scheme was being developed and was a strong critic of the Gillard government for not making clear early on how the NDIS would be funded. She also argued strongly for funding for disability advocacy services, drawing on her own experience as the mum of a daughter with Down Syndrome.

“Advocacy is vital for many people with a disability. It helps them negotiate the bureaucratic labyrinth of care and it fights for and protects their rights. Sometimes advocacy services are the sole voice of people with a disability.”

She also initiated an inquiry, chaired by the Greens’ Rachel Siewert and supported by Labor’s Claire Moore, into forced sterilisation of the disabled that led to a subsequent inquiry into sterilisation of intersex people (on which she made another excellent speech in March).

She has also been a persistent critic of her party’s failure to get more women elected. In 2012, she urged a target of 30% of female candidates, and last year declared herself “shocked and embarrassed” by the presence of only one woman in cabinet, saying it reflected “a systemic problem for our party”.

Boyce is the kind of politician that too few voters see, the sort who would make Australians feel more positively about their elected officials if they did: one prepared to grapple intelligently with policy issues and act on her principles, one prepared to take her responsibility as a senator seriously and work with others to undertake the sort of work other arms of government will never do, but that can change lives for the better. Australia is the poorer for her departure from public life.