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."
Dundee United manager Jackie McNamara hailed the capture of a player he hopes will contribute to the club on and off the field.
"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 signed off on his Shandong Luneng career in memorable fashion, scoring in the 95th minute of the Chinese FA Cup final second leg to seal a 5-4 aggregate victory over Jiangsu Sainty.
His fellow Australia defender Curtis Good impressed on loan at Dundee United from Newcastle United during a brief spell last season.
McGowan missed out on Australia's Asian Cup squad after representing his country at the 2014 World Cup.
