Merrien was originally overlooked for a place on the capital's roads this summer after failing to dip under UKA's Olympic A-standard in last weekend's London Marathon.
The GB athlete clocked a new personal best of 2:13.41 minutes on Sunday, nearly two minutes shy of the required time of 2:12:00.
His omission, the GB team opted to leave one space unfilled for 2012 with Dave Webb and Scott Overall the two selected runners, however led to outrage on Facebook.
A 'Select Lee Merrien' campaign was started with nearly 3,000 likes garnered in less than a week since the race.
And the social networkers, and Merrien, have got their wish. UK Athletics' selection policy has a clause in which decisions can, in exceptional circumstances, be overturned.
That Merrien had run over two minutes quicker than Webb surely helped, as did the fact that the Guernsey athlete's personal-best time in London came despite spending the second half of the race running in isolation, and into a headwind.
And after seeing the decision overturned and his 2012 participation rubber stamped by the BOA Merrien said: "I am absolutely delighted to have been selected and I'd like to thank the selection panel for recognising the nature of my run at the weekend.
"I am now on a short rest break with my family and then I will resume training as I aim to put in my best ever performance in London."