Ms O'Brien, who is currently head of BBC Yorkshire, replaces Leo Devine who has been appointed head of journalism production with the BBC nations and regions central team.
Ms O'Brien joined the BBC while she was still at university. After completing the BBC journalism course, she worked for several local radio stations throughout the country before moving onto Midlands Today.
In 1994, she moved on to work for North West Tonight and started producing the programme a few years later - becoming editor in 2000.
She was appointed head of BBC Yorkshire in April 2004, and is moving back to Manchester after a two-year stint in Leeds.
She said: "I couldn't resist the chance to come back to Manchester especially at this exciting time for the BBC in the North West.
"I am sad to be leaving Leeds and the great team who work in West Yorkshire but the opportunity to return to the area where I spent 10 wonderful years is too good to pass up."
Andy Griffee, BBC controller English regions, said: "Tamsin has been an incredibly successful leader for the BBC in Leeds and I'm delighted that she will now have the opportunity to bring her skill and experience to managing our local TV, radio and online services in the North West at such an important crossroads with exciting plans for the BBC's expansion in the region firmly in the pipeline."
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