If she had been successful the Department of Health would have had to order pharmacists across the country to stop selling the morning-after pill immediately.
Family values campaigner Conservative Baroness Young had tried to halt sales which began earlier this month.
Pharmacists have been allowed to sell emergency contraceptive pills without a doctor's prescription as part of government efforts to reduce the number of unwanted pregnancies.
She was also concerned that there was growing evidence that under-16s were buying the pill for £20 a pack.
Bishops' backing
Junior Health Minister Lord Hunt of Kings Heath said all the pharmaceutical associations and groups backed over-the-counter sales and it was the most effective way of preventing more unwanted pregnancies.
He said he had seen no evidence to suggest the availability of the morning-after pill would lead to a rise in sexual disease.
Lady Young attempted to use a little known Parliamentary device to ban the emergency pill sales.
If she had been successful the Department of Health would have had to order pharmacists across the country to stop selling the morning-after pill immediately.
The Lords defeated Lady Young's motion by 177 votes to 95, a majority of 82.
Lady Young's opposition included two Bishops as well as Liberal Democrats and Labour peers, who mostly argued that it was better girls should take the pill after unprotected sex, than risk an abortion or an unwanted pregnancy.
'Fornication and adultery'
The Bishop of St Albans, the Right Reverend Christopher Herbert, said: "In this particular debate, I am prepared to acknowledge that the morning -after pill may be the lesser of two evils.
"Better this form of contraception, than a steady rise in abortion."
Lady Young was supported by Labour veteran Lord Longford who said he could not support a policy which would make a rise in "fornication and adultery" more likely.
After the vote, Lady Young said she was disappointed by the stand the bishops had taken.
"When the Pope went to Ireland he was told that the IRA were protecting the Roman Catholic population against Protestant oppression and his reply was quite simply 'Murder is Murder'," she said.
"I do think we need to keep a firm hold on moral principles when we are talking about these matters."
Pill risk
Opposition front bench spokesman Earl Howe, supporting Lady Young, said many pharmacists were "alarmed" at having to sell morning-after pills.
He said pharmacists who took the trouble to ask lengthy questions would result in girls going to shops where there would be the least hassle.
He was also concerned that the pharmacists' checklist of questions to ask the girls did not mention ectopic pregnancy, one of the main risks of taking the morning-after pill.
The President of the Family Planning Association, Labour's Baroness Gould of Potternewton, argued that easy access to the pill was "absolutely essential" for women who might find it difficult to get a GP appointment within 72 hours.
She said they were not "irresponsible, reckless or promiscuous", but women whose normal contraception had failed.