Windsor was an independent member for the New South Wales Legislative Assembly seat of Tamworth from 1991 to 2001 − supporting the incumbent Greiner Liberal/National Coalition minority government at the 1991 election.

He subsequently entered federal politics, serving as an independent member for the Australian House of Representatives seat of New England from 2001 until retiring in 2013 − supporting the incumbent Gillard Labor minority government at the 2010 election.

Windsor was one of the four independents who held the balance of power after Nick Greiner's Liberal-National Coalition lost 10 seats, resulting in a hung parliament.

After an adverse ruling by the Independent Commission Against Corruption against Greiner for offering former minister Terry Metherell a patronage job, the Labor opposition tabled a motion of no confidence in the government.

In September 2004, in an interview with Tony Vermeer from The Sunday Telegraph,[9] Windsor was the centre of controversy over an alleged breach of the Commonwealth Electoral Act.

A month later, speaking under parliamentary privilege, he said that National Party leader John Anderson and Senator Sandy Macdonald had made the offer through an intermediary, Tamworth businessman Greg McGuire.

[16][17] In a press conference on 7 September 2010, Windsor revealed that he would support the incumbent Labor government during confidence motions and supply bills.

"[26] In an interview published in The Sydney Morning Herald following the 2010 federal election, it was reported that Windsor supports a rent resources tax, deep cuts to carbon emissions, and improved services to rural and regional areas such as Labor's proposed National Broadband Network but wants to ensure the scheme is fully costed.

[1] He has fought a long-standing battle protecting the interests of local landholders and farmers living on one of NSW's richest agricultural regions, the Liverpool Plains, due to the impact of mining on underlying groundwater.

[27] During the 2010 federal election campaign, it was revealed that Windsor had sold his family farm at Werris Creek to a wholly owned subsidiary of Whitehaven Coal, and then leased the property back.

[28] The Australian subsequently claimed that Windsor yielded a return about three times greater than other farmers who sold their properties to the same company in the previous 18 months.

[31] He subsequently announced that he was supporting Gillard's carbon policy, as a matter of principle, and stated: "This is about the history of people, most of whom haven't even been born yet.