Macri, elected in 2015 at the head of a center-right coalition, has battled for months to stabilize South America's third largest economy, but his dwindling popularity means he is fighting an uphill battle for re-election next year.
"Let's hope we make a good impression," the 59-year-old president said in a video message Thursday on Twitter as he prepared for a series of bilateral meetings on the eve of the summit.
A $56 billion International Monetary Fund bailout has bought his government time but left it little scope to shape fiscal policy, forcing it to deepen unpopular spending cuts in order to turn in a balanced budget next year.
Noisy street protests outside his Casa Rosada government offices are a near-daily occurrence, and general strikes have twice ground the country to a halt in recent months.
Far from showcasing its economic opening to the world, the week of the summit has instead seen public transport workers halt metro and bus services while a one-day strike by national airline Aerolineas Argentinas brought chaos for travelers.
Shop window
"The expectations of the Macri government, when it agreed to host the summit in Buenos Aires, was that it would serve as a shop window to show off its policy of gradual reforms," said Bruno Binetti, international relations expert at Buenos Aires' Torcuato University.
"Argentina then was good news internationally, with its pro-market policies getting popular support," said Binetti.
His Cambiemos -- "Let's Change" - coalition swept aside exchange controls, and generally opened up Argentina to foreign trade and investment after years of market isolation that followed Argentina's 2001 financial crash.
But the initial optimism that greeted Macri's election has all but evaporated.
South America's third largest economy has struggled to recover after a massive currency crisis that saw the peso lose half its value against the dollar.
Inflation is running at 45 percent and with the economy shrinking 2.6 percent in 2018, according to the IMF.
When late president Nestor Kirchner hosted Argentina's last major political gathering -- the Summit of the Americas in 2005 -- he was part of a group of vociferous leftist Latin American leaders including Hugo Chavez, who formed a bold front against US President George Bush.
Thirteen years on the political landscape is much changed, and the irony is that a pro-trade, deregulation-friendly Argentine president finds himself surrounded at the G20 by a powerful nucleous of populist and protectionist leaders led by US President Donald Trump.
Mass protests
Mass protests are expected on the streets of Buenos Aires on Friday, where more than 20,000 security forces have been deployed to protect the leaders.
"The G20 is going to last a day. The second day, they are all going to go away because of incidents are going to go off. People are hungry and they're staging a G20 here?" said Jesus Olgin, a street vendor in the center of Buenos Aires.
Macri will strive to use the summit to sway foreign investors to get involved in the Argentine economy, according to political scientist Rosendo Fraga.
To that end meetings are planned with his US counterpart Donald Trump, as well as those of China, France, Russia, Japan, Britain and Germany.
"In these meetings, Argentina will get support and praise. While the multilateral economic and trade framework is getting weaker, bilateral relations are strengthening," said Fraga.
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