Affected staff were told on Wednesday and colleagues said they left the building with "boxes in hand".
A spokesperson for Asda said: "These changes impact around 1,100 roles across Asda House in Leeds and George House in Leicester, and sadly result in around 300 colleagues leaving us.
"Today we are making some significant changes to the way we operate our home offices. As you’d expect, we have discussed the details of these changes with our colleagues first."
Asda said the bulk of the 300 job losses will be in Leeds and the affected staff were told on Wednesday and have already left.
The firm said staff will be given compensation packages, but it is too early to say what these will be.
Of the 1,100 affected staff, the 800 who will be kept on will see their jobs change as many will be losing their line manager.
"Their job role is changing slightly," said the spokesperson.
Asked why people have lost their jobs, she added: "The market is constantly changing. Retailers have to make changes and head offices have to make changes."
Asda employs 2,500 staff at its Leeds head office.
The spokesperson said: "In recent years, the competitive landscape in retail has changed significantly and Asda has been no different. Our stores have adapted the way they operate to meet the changing needs of our customers, and our home offices must also adapt how they operate to support our stores.
"At Asda we value each and every one of our colleagues. The changes are in response to the ever changing sector in which we’re working and the need to adapt to create an agile business which is fit for the future."
The news comes after reports surfaced last month that thousands of Asda workers across 18 under-performing stores are facing redundancy or changes to their working hours.
Staffing arrangements in a further 59 stores are also being looked at.
The firm is battling against stiff competition from discounters Aldi and Lidl, which are around 15 per cent cheaper than Asda, which is the cheapest of the big four grocers.
Asda reported its first positive sales growth in three years last month, driven by food price inflation and lower prices.
It said like-for-like sales rose 1.8 per cent in the three months to June 30
This was the first positive quarter after 11 consecutive quarters of diminishing sales as shoppers have fled to discounters Aldi and Lidl. It was also a vast improvement on the 7.5 per cent fall that Asda reported this time last year.
Asda has been the worst performer of the big four for some time although there have been signs of improvement recently.
Its new CEO Sean Clarke is credited with reducing prices, getting rid of superfluous stock and introducing discount level brands such as Farm Stores.