City Hall's move to Newham has been confirmed for January, mayor of London Sadiq Khan has revealed.
The Crystal will host the London Assembly in a move from its iconic Norman Foster-designed building on the south bank of the Thames.
Mr Khan said the relocation will save £61 million over the course of five years, which he has pledged to spend on frontline services such as the Met Police and London Fire Brigade.
The Greater London Authority (GLA) owns the Crystal but said it rented its current home to the tune of more than £11million a year from the Kuwaiti government.
Unmesh Desai, London Assembly member for City and East, described it as "very expensive".
He said it had been emotional to bid the current City Hall farewell.
"I still remember the excitement and sense of privilege that I felt walking into the building for the first time after being elected to represent the City and East constituency in 2016.
“As I have always said, London is moving east.
"I will be keen to see how having the beating heart of London politics in Newham might give a boost to the regeneration of the Royal Docks and I will continue to call for more much-needed investment and job opportunities in the area."
The final meeting at the current City Hall is on December 2, with the GLA then moving out and being based temporarily at its Union Street offices for a few weeks while work is completed at the Crystal.
Its first meeting at the Royal Docks venue will be Mayor's Question Time on January 20, where Mr Khan is quizzed by members of the assembly.
The Conservative opposition on the GLA felt London's government has been "left in limbo" and called the switch to the Crystal "deeply uninspiring".
Mr Khan believes the move, along with the proposed opening of the Elizabeth line next year, will act as a catalyst for the regeneration of the Royal Docks.
He said: “City Hall’s move to The Crystal will usher in a new era for the GLA and this flourishing part of east London."
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