The £11 billion merger between Standard Life and Aberdeen Asset Management is complete, with the tie-up creating Europe's second-biggest fund manager.
A Stock Exchange announcement on Monday confirmed the deal's conclusion, and follows on from court approval for the merger last week.
Co-chief executive Keith Skeoch described the combination as the "beginning of a new chapter" in the companies' history, and confirmed that the new entity will trade as Standard Life Aberdeen.
"Today marks the culmination of many months of hard work and preparation by our business and the beginning of a new chapter in our history as Standard Life Aberdeen.
"Our leadership team is in place and we have full business readiness from day one," he said.
The enlarged company will be jointly headed up by Mr Skeoch and Aberdeen boss Martin Gilbert, and Standard Life Aberdeen will hold £670 billion under management.
The merger, which was agreed in March, is targeting cost savings of £200 million a year, with around 800 jobs expected to be lost over a three-year period from a global workforce of 9,000.
Mr Gilbert said: "As ever our priority remains the delivery of strong investment performance and the highest level of client service.
"The merger deepens and broadens our investment capabilities and gives us a stronger and more diverse range of investment management skills as well as significant scale across asset classes and geographies."
Overall, Standard Life Aberdeen will have offices in 50 cities around the world, servicing clients in 80 countries.