It aims to hire 33,000 additional workers for the Christmas period - two-thirds more than usual.
The postal service typically employs between 15,000 and 23,000 extra staff between October and January.
The temporary workers will mainly work in sorting offices, delivery vans and data centres.
Royal Mail says that a higher number of workers is needed to help sort Christmas deliveries of letters, cards and parcels this year because many consumers are staying at home under Covid-19 restrictions and shopping online.
More than 13,000 mail centre sorting posts are available in England, about 1,400 posts in Scotland, 700 posts in Wales and 500 posts in Northern Ireland.
The temporary workers will support more than 115,000 postmen and women in permanent roles. About 1,000 of the new recruits will work for the company's new Covid-19 testing kit collection team.
The Royal Mail's Sally Ashford said: "During these unprecedented times we believe it is critical that Royal Mail continues to deliver.
"We want to do our best to deliver Christmas for our customers and support the effort on the pandemic.
"This helps the whole country to celebrate and stay safe during these difficult times."
Royal Mail has been trying to capitalise on the rise in online shopping, which has been accelerated by the coronavirus crisis.
Earlier in October, the firm announced it would start collecting parcels and mail from people's homes.
Its "Parcel Collect" service, which has been trialled in parts of the west of England, will be available every day except Sunday, and there will be a 72p charge per parcel, plus postage costs.
Pre-paid return packages can be collected for 60p per item.
The new scheme will help online shoppers send back unwanted items and was described by Royal Mail as "one of the biggest changes to the daily delivery since the launch of the post box in 1852."
The wider online retail industry has also been gearing up for an uptick in demand for deliveries in the run-up to Christmas.
In September, the industry body for online retailers warned that firms may struggle to cope if consumers leave ordering presents until the last minute.
Andy Malcahy of the IMRG stressed that there was no need for shoppers to panic buy, but said: "If you can spread out your shopping and do quite a lot of it in November, maybe even a bit of it now, then that would really help."
Mike Hancox, boss of the delivery firm Yodel, also told the BBC: "It's been like Christmas for the last six months for us".
It is adding 2,500 self-employed drivers and nearly 500 staff in its sorting centres across the UK to bolter its operations.
"We think it will be the biggest online Christmas ever, by some way," Mr Hancox said. "Certainly at Yodel it will be our biggest ever year. We're planning for success and I think every other delivery carrier will be expecting the same."
Royal Mail has seen parcel deliveries increase in recent years but is still on track to make a loss in 2020.
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