Couples are vying to be the first to complete their vows, with ceremonies lined up at midnight in some areas.
It is not known for certain how many couples will tie the knot beyond the numbers who have declared their intentions in the first few weeks of the new law being in place.
The government says its best estimate is that there will be a combined figure of 6,000 same sex marriages and civil partnerships every year - but it does not break down that number between the two options.
One campaigner estimated that there could be about 500 gay wedding services taking place this Saturday and Sunday.
Civil partnerships were introduced in 2005 and give many of the same legal and financial protections as marriage.
There were 6,362 civil partnerships formed in England and Wales in 2012, the Department for Culture, Media and Sport said.
A government spokeswoman said: "We expect the number of marriages of same sex couples and civil partnerships combined, when they are both available, to be broadly the same as the current number of civil partnerships.
According to the most recent data available, the councils registering the most civil partnerships are Westminster in London (224 in 2012) and Brighton and Hove (220).
Westminster Council already has 52 same sex marriages lined up, including four on Saturday. Brighton and Hove Council said five same sex couples would marry on Saturday alone.
The government spokeswoman said that a "short-term surge" had been anticipated in the weeks following the option of marriage being made available to same sex couples.
Pink News publisher Benjamin Cohen, who founded the Out4Marriage campaign, said he did not expect "humongous numbers" of weddings over the weekend, guessing there would be "something like 500 or so".
"People have not had had long to prepare for it", he said, pointing to the fact that the government only announced the date in December.
Another factor is that couples already in civil partnerships are not yet able to convert to marriages. The government, which put this down to legal technicalities, is hoping to remove this hurdle by the end of the year.
A number of other couples will have put off entering into a civil partnership until the marriage law came into force, Mr Cohen said.
Legislation allowing gay marriage was passed in Scotland in February and the first same sex ceremonies are expected to take place in October. Northern Ireland has no plans to change its current law which does not allow same sex marriages.
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