The 26-year-old is expected to play five games for the Sixers before joining up with England's limited-overs squad in India.
"To get the opportunity to play at the SCG is obviously a massive ambition of mine," he told the club website.
Roy could make his debut in the game against Sydney Thunder on 20 December.
He played three Big Bash games for Thunder two seasons ago.
"Jason is known as an explosive weapon at the top of the order and we look forward to his contribution, bringing also his English experiences from which we can share," said Sixers head coach Greg Shipperd.
England begin the limited-overs section of their tour to India next month.
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She said, if the party was re-elected in May's Scottish Parliament election, it would introduce a more "progressive" local tax from April 2017.
The reforms could see councils given a share of income tax revenues in an effort to give them an "incentive" to boost economic growth.
Last year, a commission on reform called for a "more progressive" tax.
The Commission on Local Tax Reform did not recommend a single alternative but it suggested there could be merit in combining a property-based levy with an element of income tax.
The current council tax charges householders on the value of the property they live in. The rate it is charged at has been frozen by the Scottish government since 2007.
Speaking at the David Hume Institute in Edinburgh, Ms Sturgeon said: "The report from the cross-party Commission on Local Tax Reform made clear that now is the time to reform local taxation.
"The commission argued for measures which will make council tax more progressive, and which will give greater assistance to people on lower incomes.
"So next week we will set out details of how we intend to achieve this from April 2017 onwards.
"These changes will be part of a longer term plan to increase the accountability of local councils to the populations they serve."
Discussions with local authorities are expected to determine how the Scottish Parliament can gain more power over income tax and local authorities can secure a share of income tax revenues for their area.
Asked if councils should be given power over sales and tourism taxes, as recommended by the commission, Ms Sturgeon said priority would be given to the assignation of income tax and other council tax powers would be considered.
"Scotland is a small country and I think it is right that we take steps to incentivise local authorities to boost economic growth in their own areas, but equally I think we have got to be careful about creating a postcode lottery in terms of tax rates in different local authority areas."

The 32-year-old former Namibia captain has made 113 appearances since joining Sarries in 2009 and helped the club win two Premiership titles.
Burger, who won 41 caps and appeared at the 2015 World Cup, will return to Namibia to become a farmer.
"It is sad that it's coming to an end but playing rugby is something that I have really loved doing," he said.
"Growing up I wanted to be a professional rugby player and I have been fortunate to live that dream."
Saracens director of rugby Mark McCall described Burger, who leaves just two weeks before the Champions Cup final and the start of Sarries' Premiership play-off campaign, as "an amazing player and person".
"He set a phenomenal example on the field with his bravery and the way that he gave everything he could in every game," McCall told the club website.
"He will always be remembered as one of the true greats of Saracens."

15 May 2017 Last updated at 13:14 BST
The narwhal is a mysterious member of the whale family that mostly lives in the Arctic.
It has a long pointy tusk that points out of the end of its nose - that's led to the creature having the nickname, the "unicorn whale".
Scientist knew very little about what these tusks were for until they started filming them in the wild, using drones.
Now they know it's part of a clever way to hunt fish...
Watch this...
Surrey and England batsman Jason Roy has agreed a short-term deal to play for Sydney Sixers in the forthcoming Big Bash tournament in Australia.
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The SNP will set out details of its plans on council tax reform next week, First Minister Nicola Sturgeon said.
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Saracens back row Jacques Burger will retire from rugby after Sunday's Premiership game against Newcastle.
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Scientists reckon they've figured out why the narwhal has its famous tusk.