McGowan, 25, previously spent five years with Hearts between 2008 and 2013, winning the Scottish Cup in 2012.
Capable of playing at right-back and centre-back, the 12-cap Australia international has agreed a deal at Tannadice Park until the end of 2015-16, his contract with the Chinese Super League's Shandong having expired late last year.
"It is great to be back in the Scottish Premiership and I am excited about the challenge of being a Dundee United player," McGowan said in a statement.
"When I moved to Shandong Luneng Taishan, I believed I would return to Scottish football one day and for it to be here at Tannadice is fantastic.
"My time in China was a great experience but I look at what we can achieve here at Dundee United this season and I want to play a part in helping the club reach its goals."
"Ryan is a tough, strong and excellent footballer, who will improve us defensively," he said.
"He is a big lad, who is strong in the air, and this will impact in both defensive and attacking scenarios. He is a strong personality, which is important for me.
"I am delighted to be able to bring him to United because other clubs were after him. Players see our club as a great place to show off their talent and enjoy playing football.
"This signing makes us stronger defensively and that was something I was keen to address in this transfer window."
McGowan missed out on Australia's Asian Cup squad after representing his country at the 2014 World Cup.
