He makes the case for Ken in Wednesday's Guardian, acknowledging that he considered whether to enter the race himself.
Lammy has also nominated Diane Abbott for Labour leader - in the interests of the contest. But I would guess he will vote for David Miliband, which may perhaps disappoint those who may have begun to detect the seeds of the sharpest swing leftwards from a New Labour position since the young technocratic minister Anthony Wedgewood Benn became plain Tony, tribune of the left.
Former Bethnal Green MP Oona King is also seeking the nomination. It is unclear whether anybody else will join the race, though many other candidates have been mooted - including Alan Johnson, Jon Cruddas and James Purnell, as well as the rather more fantastical prospect of Lord Mandelson seeking to tread in his grandfather's LCC footsteps.
The Standard's Paul Waugh tweets:
DLammy will chair Red Ken's campaign 4 Lab mayoral candidate. Not an fan of Oona King, clearly. Cd help his own 2016 chances tho
Lammy's challenge on the Livingstone campaign - in the party and in the 2012 race if Livingstone does prevail - will be to prove wrong those who believe Labour could play into Tory hands by re-running the 2008 race.
I suspect that the nomination timetable - running concurrently with the Labour Party leadership contest could seriously reduce further the chances of any candidate successfully challenging the favourite Livingstone, who will expect to poll particularly strongly in the affiliates section of the electoral college. Had the race begun after the party conference this Autumn, there would have been a great deal more attention paid to the nomination race by party members and supporters in London.
As much as a third of the Labour party's national membership is in London, but the Mayoral nomination race now risks being very much be a second-order contest. There will be fewer events and hustings, much less media coverage and less focus from party members than would have been the case if the two races were not taking place at the same time. (And it may well be that Labour may now find it more difficult fully maximise the opportunity to use the Mayoral nomination as a second focus for a recruitment drive, and particularly to connect with new citizens' movements in the capital).
It would take quite a conspiracy theorist to suggest that the Labour NEC had sought to atone for its sins of the 2000 nomination process by this time stitching this thing up for Ken Livingstone.
But I suspect that a much more prosaic reason - the adminstrative cost of balloting the members separately, given the parlous state of Labour's finances - might well have helped to achieve much the same pro-Ken outcome.