The Italian World Cup winner, who was released in May after 19 years at Juventus, said in Turin on Wednesday that he was joining the A-League club in a two-year contract that Australian media reported was worth A$2 million a year.
"Last night's signing of Alessandro Del Piero is a big moment for this club and, we believe, a historic moment for football in Australia," Barlow said on the pitch at the Sydney Football Stadium.
"I wouldn't like to go into the details of the contract," he added. "But this does represent the largest professional sporting contract in Australian history and the numbers that have been discussed aren't too far off the mark."
Del Piero, 37, is undoubtedly the biggest name to join an Australian club and his signing was warmly welcomed in the local media.
"He's ours!", screamed the back page of the tabloid Daily Telegraph, while inside a column penned by Socceroo and Del Piero's new team-mate Brett Emerton was headlined "Our greatest day".
"It's hard to express how big this deal is for the city, the club and the league," the former Blackburn Rovers midfielder wrote.
"Alessandro is one of the all time greats of world football and his signing will really put us on the map in an even bigger way than Dwight Yorke and Robbie Fowler did before him."
Thursday's newspapers also illustrated the challenge that faces football in Australia's crowded sports market with stories about rugby league and Australian Rules still dominating the back pages.
Football, once riven by ethnic rivalries, has progressed since the formation of the A-League in 2005 but still trails the rival codes in popularity.
Football Federation Australia, whose task it is to close that gap and who are in the process of negotiating a new television deal, also welcomed the arrival of the 91-cap international.
"Undoubtedly, this signing will have an immediate impact on attendances, membership, TV ratings and corporate support for the club and the A-League," said FFA chief executive Ben Buckley.
"The A-League's image and reputation will grow across Europe and Asia, in particular.
"While this impact is not as immediate as the other commercial measures, the benefits will ultimately flow to the brand value of the A-League, its clubs and our corporate partners.
Barlow said he hoped Del Piero's arrival would inspire a new generation of supporters for Sydney FC, who averaged 11,861 fans per match at the SFS last season.
"Alessandro had many, many outstanding offers from big clubs around the world but in weighing up those opportunities, he felt Sydney FC was the right one for him," he said.
"I think that he chose us says a lot about this club and a lot about football in this country and how it has moved on in recent years.
"He's 37 but he's a world class football player and still able to play at the very highest level and that's evidenced by the fact that there was so much interest in him from clubs in the English Premier League, Serie A and others.
"Beyond the footballing perspective, clearly he is a major icon of the game and he can have an impact on us as a club both on and off the pitch."
Del Piero is expected to arrive in Sydney in eight or nine days, Barlow said.
The new A-League season begins in early October with twice champions Sydney FC opening their campaign in New Zealand against Wellington Phoenix on October 6.