The plebiscite was engineered by Tony Abbott in 2015 and adopted by Mr Turnbull when he took the leadership to satisfy the progressive and conservative wings of the Coalition. Prime Minister Malcolm Turnbull on the final day of the election campaign. Credit:Andrew Meares The management of the vote and the potential for Coalition disunity over the issue shapes as a key early test for Mr Turnbull if he is returned - particularly if he only just scrapes home on Saturday night. The final Fairfax-Ipsos poll of the campaign - which found the major parties locked 50-50 in the two-party preferred vote, found seven in 10 Australian voters backed a change to the Marriage Act to allow same-sex couples to wed. This figure represents a rise from 69 per cent in August 2015, and 57 per cent in November 2010. Just 22 per cent of voters now same-sex marriage, down from 25 per cent in August 2015 and 37 per cent in November 2010.

Support for the reform is broad-based, too: a majority of Coalition voters (58 per cent), Labor voters (79 per cent) and Greens voters (97 per cent) back the change. Bill Shorten declared that the election would be "a referendum on the future of Medicare". Credit:Alex Ellinghausen Mr Shorten hardened his position in favour of a parliamentary vote during the campaign, promising a Labor government would legislate the reform as its first priority. The Prime Minister insisted a change to the Marriage Act would "sail through Parliament" later this year, despite being forced to concede Coalition MPs opposed to change will not be bound to support the outcome of the plebiscite. Illustration: Ron Tandberg

Despite the apparent popularity of voters having their say, Australian Marriage Equality director Marriage Rodney Croome questioned the need for the $160 million plebiscite and warned it could unleash hate towards gay people. "I am hopeful the next Parliament will have a clear majority of members who favour marriage equality making a free vote the obvious way forward," he told Fairfax Media. But on the final day of the marathon eight-week campaign, focus shifted from same-sex marriage to health after Mr Turnbull gave a late "guarantee" on morning television that voters would not pay more to see the doctor because of the Coalition's decision to freeze the GP rebate. With Labor hopes of big swings in Queensland fading, marginal seats in New South Wales on a knife edge and the firefighters dispute in Victoria dampening ALP prospects there, Mr Shorten leapt on Mr Turnbull's claim to point out the Australian Medical Association has warned that doctors were at "breaking point" because of the freeze. Mr Turnbull later argued that bulk-billing was at an all-time high despite the freeze beginning in 2013 under Labor.

While the Coalition's re-election pitch of stability and economic competence has appeared to resonate with voters in the final week of the campaign, Labor's message about protecting Medicare and the healthcare system has also hit home, leaving plenty of seats in play on polling day. While national polls continue to suggest Mr Shorten is within striking distance of the 76 seats needed for a potentially historic win, few on either side of politics believe enough marginal seats will change hands once votes are counted to see the Coalition thrown out. A slew of Coalition seats remain in play including the NSW seats of Macarthur, Eden-Monaro, Page and Dobell, while Solomon in the NT and Capricornia, Petrie and possibly Flynn in Queensland could fall. The Nationals were toey about the threat posed by former independents to Luke Hartsuyker in Cowper and Deputy Prime Minister Barnaby Joyce in New England. The Coalition-held seats of Mayo, Grey and Hindmarsh in South Australia were said to be under threat from Nick Xenophon's NXT candidates.

But offsetting that, Labor is nervous about going backwards given late Coalition confidence in some seats such as Werriwa and Greenway in New South Wales, Chisholm in Victoria. The Labor-held Melbourne seat of Batman is also under threat from the Greens. Mr Turnbull again told voters on Friday not to risk a minority government but to choose "stability, leadership, a strong Coalition majority government and the national economic plan that is delivering strong growth and jobs". Despite Labor morale taking a late hit when elder statesman Bob Hawke predicted a Coalition win, Mr Shorten continued to push his Medicare campaign and promises to provide more funding for schools, hospitals, TAFE and universities. "I am determined to win the election . . . Labor's been on a journey for the last three years, three years ago we were not united, and now we are. We have put forward a policy agenda," he said.