A majority of 86.68% of savers and 85.44% of borrowers passed the resolutions to merge with Chelsea.
Bringing the two organisations together will create a second major force in the building society sector. The enlarged society will have capital ratios amongst the strongest of any major UK lender, bank or building society and a secure funding base.
The merged society will have 2.7million members, assets of £35 billion and a national network of 178 branches.
Iain Cornish, chief executive of Yorkshire Building Society, said: "I am delighted that both our members and the Chelsea members have recognised the benefits of this merger and voted in favour of it.
"The financial services market has changed fundamentally over the last two years and scale is increasingly important to the efficient operation of building societies and access to funding markets. Our members can, however, be assured that we will not become too big to offer the personal service which we pride ourselves on. "
The merger, subject to confirmation by the FSA, will complete on 1st April 2010.
