Although the exterior of the building, originally opened at the north-west London venue in 1890, appeared unaltered there have been significant changes with the creation of a new roof terrace viewing area the most striking following seven months of work.
Meanwhile the main Long Room, through which the players walk before taking the field, has undergone major restoration.
The building was re-opened by Tom Graveney, the former England batsman and now president of Lord's owners Marylebone Cricket Club (MCC) together with England 'A' batsman Alistair Cook.
The 20-year-old Cook was in the MCC team due to play County champions Warwickshire, in the traditional curtain raiser match to the English season, starting at Lord's on Friday.
Graveney said: "I'm delighted that MCC has restored the Pavilion - one of the most famous buildings in world sport - to pristine condition.
"I first played here more than half a century ago and, quite simply, I've never seen the Pavilion looking better."
Organisers of London's bid for the 2012 Olympics hope to stage the archery competition at Lord's.
Bid chairman Sebastian Coe, the 1500 metre Olympic gold medallist at both the 1980 and 1984 Games, added: "The Pavilion would provide a unique backdrop for Olympic archery in 2012, and it's fantastic to see this beautiful building restored.
"Lord's perfectly encapsulates London's mix of past and future - with the historic Pavilion at one end and the futuristic Media Centre at the other."
However, for all the money spent on updating the Pavilion, one tradition remained intact. There was no play at Lord's on Friday, the first day of a four-day match, because of rain.