An opinion poll released on Friday indicated Mr Miles faced defeat at the state election, with the opposition tipped to win an extra 18 seats and a majority government.
The premier's rivals the Liberal National Party led the two-party preferred vote 54 per cent to 46 per cent in the poll published by News Corp.
However, Mr Miles is set to get a better idea of his Labor government's election hopes on Saturday.
By-elections will be held at two traditional Labor strongholds: Ipswich West and Inala, the seat of former Queensland premier Annastacia Palaszczuk.
Margie Nightingale is Labor's candidate for Inala and faces the LNP's Trang Yen. (Darren England/AAP PHOTOS)
"Winning Ipswich West will be very, very hard. I've been saying that every day and you guys haven't believed me," Mr Miles told reporters.
"Now you have a poll which suggests that there is a very substantial swing so you should expect to see that (on Saturday)."
About a third of voters have already made up their minds and submitted their decision before election day across both seats, according to the Queensland Electoral Commission.
History will be made by whoever wins at Inala, considered Queensland's safest Labor seat.
It will mark the first time Inala will not be represented by a Palaszczuk family member.
Contested for the first time in 1992, the electorate was initially represented by Ms Palaszczuk's father Henry.
He went on to become a senior minister before being succeeded by his daughter who resigned in December, with Mr Miles taking the reins.
"Inala is a slightly different race, the margin is much higher but it's inflated by the fact that they had the premier in their seat and that tends to deliver support," Mr Miles said.
"We would expect a very big swing also in Inala but ... there's more chance that we will win there."
An Ipswich West by-election was triggered by Labor MP Jim Madden departing in January.
Annastacia Palaszczuk and her father Henry held the seat of Inala since its formation in 1992. (Jono Searle/AAP PHOTOS)
He will run for Ipswich council election in Saturday's Queensland local government elections.
The Miles government's margin in Ipswich West after the 2020 poll was 14.3 per cent.
At Inala, the margin was a staggering 28.2 per cent thanks to Ms Palaszczuk's popularity.
Since 1992, average swings against Labor at by-elections when they are in government is five per cent.
Opposition Leader David Crisafulli hoped the by-election results sent a message to the Labor government ahead of the October poll.
"We're dealing with seats in Labor Party heartland ... so we understand the mountainous task ahead," he said.
"(The by-elections) can't change the government but my goodness they can send a message on behalf of every Queenslander that things aren't right in this glorious state."
Margie Nightingale is Labor's candidate for Inala and faces the LNP's Trang Yen.
Wendy Bourne is running for Labor in Ipswich West against the LNP's Darren Zanow.
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