It is the first time that the firm has been retained by the company.
It is believed to be the first time Norwich Union has handled property investments for someone else.
Before being taken over by Norwich Union the council's pension fund direct portfolio was run by another company, which used Clifford Chance for legal advice.
Deborah Lloyd, the commercial property partner at Nabarros who led the tender, says that the contract is a big win.
She says: “For us this is more an issue of the fact that it's Norwich Union rather than the size of the work.
“The value of the portfolio is not particularly high, but Norwich Union doesn't put out an enormous amount of work and this is a new area of business for them.
“This is the first time we have been retained by them, and they will be looking for other portfolios to manage in the future so it is a good opportunity for us to develop a relationship with them.”
Commercial property partner Bernadette Horan was also part of the firm's six-strong team bidding for the work.
Nabarros has worked for Norwich Union before on one-off investments, and it advises Quercus Property Partnership and Norwich Union Mill PFI fund – two joint ventures in which the company has a stake.