By Mathieu Rosemain and Gwénaëlle Barzic
The Paris-based group, controlled by billionaire Vincent Bollore, had made little progress since telling markets a year ago that it would sell part of UMG, unnerving investors and leaving equity analysts scrambling to value the asset.
But Vivendi confirmed in a statement on Thursday it had now selected the investment banks, without naming them, to start the formal process of a sale of a minority stake, which the group said should be finalised by the start of next year.
"There's no need to rush, we're taking things step by step," Chief Executive Officer Arnaud de Puyfontaine said in a call with analysts.
Valuation estimates for Universal have varied from 17 billion euros (£15.2 billion) from Redburn to 44 billion euros from JP Morgan.
The music label, the world's biggest ahead of Sony Music Entertainment and Warner Music and home to artists like Taylor Swift, Drake and Lady Gaga, was the key driver of growth for Vivendi in the first half.
The group's core operating profit jumped by 28% from a year earlier on a comparable basis to 718 million euros, driven by 44% growth in earnings before interest, tax and amortisation at UMG.
Group revenues rose 6.7% to 7.35 billion euros.
Universal is tapping public thirst for subscription and ad-based music streaming services, on top of a rebound in physical sales of compact discs, fuelled notably by the success of "Bohemian Rhapsody", the 2018 biopic of Queen's lead band singer Freddie Mercury.
After a 15-year downturn, the music industry has rebounded with global recorded music revenues increasing by 9.7% in 2018 to $19.1 billion (£15.3 billion) - the fourth straight year of growth, according to the record industry trade group IFPI.
De Puyfontaine said on the analyst call that Vivendi would use proceeds of the sale of up to 50% of the UMG for bolt-on acquisitions and "significant" share buybacks.
In a statement Vivendi said, without elaborating, that several contacts had already been made with potential strategic partners.
Universal's strong results contrast with those of Vivendi's second-biggest division, pay-TV Canal Plus, where first-half revenue fell by 2.2%.
The TV unit, which plans to cut about 18% of its staff in France, has been losing subscribers in its home country as it faces competition from streaming platform Netflix.
It also suffered a heavy blow last year when it ended up empty-handed in a crucial football rights auction in France, beaten by Spain's Mediapro.
(Reporting by Mathieu Rosemain and Gwenaelle Barzic; editing by Michel Rose and Kirsten Donovan)
By Mathieu Rosemain and GwÃ©naÃ«lle Barzic