The sports retailer said that 60.4% of shareholders voted in favour of the bonus scheme, which had been presented for a third time after investors had previously fought against it.
The plan has drawn fire because it does not detail what proportion of shares will be vested to Ashley, who has sold hundreds of millions of pounds worth of Sports Direct shares in the past.
Keith Hellawell, chairman of Sports Direct, said: "On behalf of the entire board, I would like to thank our shareholders for their support and participation in this process.
"The board and the remuneration committee responded to the feedback received from shareholders and today's vote in favour of the resolution will ensure that the group continues to retain and motivate its hard-working employees.
"The resolution today also recognises the substantial contribution made by Mike Ashley over many years and, as demonstrated by the previous schemes, has the potential to create a further significant increase in shareholder value."
The latest plan is linked to a company-wide scheme that would hand members 25 million free shares if the firm doubles earnings by 2019.
The approval comes hours after the Pensions & Investment Research Consultants (PIRC) urged shareholders to rally against pay and bonus plans at some of Britain's biggest retailers including Sports Direct.
PIRC, Europe's largest independent corporate governance and shareholder advisory consultancy, said it supports the "oppose" vote on Sports Direct's complex share bonus scheme and is also against pay plans at Marks & Spencer (M&S), and advises shareholders to oppose a vote on pay plans at Sainsbury.
Sports Direct had proposed giving Ashley a cash windfall of up to £73m (€90m, $122.7m) in April, but this was voted against by shareholders.
Following the rejection of his bonus in April, Ashley sold 7% of his shares which were worth over £220m.