Wiener served at the state appellate court in San Diego for 16 years; he also filled in on assignment at the California Supreme Court in San Bernadino, Calif., for three years.
"I've been retired since January 1994 and engaged in private dispute resolutions since then, and one of the activities I have had in my agenda is to get involved with an exciting, interesting, new company in the private sector," Wiener said.
The announcement comes as MP3.com is slowly putting its legal troubles behind it through expensive settlements.
The San Diego-based company has already settled with most of the Big Five record labels--BMG Entertainment, Sony Music Group, Warner Music Group and EMI Recorded Music--but it's still battling with Seagram's Universal Music Group.
A federal judge ruled last month that MP3.com willfully infringed the copyrights of the recording giant, opening the music company to potential damages of around $118 million.
Shortly after the ruling, independent music companies Zomba Recording and Zomba Music Publishing each sued MP3.com, alleging willful copyright infringement through its My.MP3.com service, which lets people listen to their CDs through any computer with Web access.
"We are very pleased to have Justice Wiener join the MP3.com board of directors and look forward to his counsel and involvement in the exciting new arena of digital music," MP3.com CEO Michael Robertson said in a statement.
Wiener currently serves as a fellow of the American College of Civil Trial Mediators, as a member of the California Academy of Appellate Lawyers, and on the board of trustees of California Western School of Law.
Although Wiener declined to comment on MP3.com's legal struggles, he said he believes his appointment is a "very exciting, worthwhile, interesting and challenging opportunity."
"I'm certainly not a guru on technology...Talking to my grandchildren and little kids around the block, they know more about listening to music on the Internet than I do," Wiener said. "So it's exciting to think that I'll now be cool with my grandchildren."