The company, founded by billionaire Newcastle United boss Mike Ashley, has seen its shares rise 86% since the start of the year.
The FTSE 100 is updated every three months, reflecting changes in the market value of companies.
The reshuffle takes effect from 23 September.
Greek coke bottler Coca Cola Hellenic is also set to join the top flight of London-listed companies after it switched its primary listing from Athens to London earlier this year.
But outsourcing firm Serco has been dropped after its shares fell 8.5% since the end of June.
It is facing an investigation into its practices, and the potential suspension of future government contracts, saw its share price plunge earlier in the summer, before recovering slightly.
Sports Direct, said in a trading update on Wednesday that sales had risen by 18.2% in the 13 weeks to the end of July, compared to the same period last year.
Retailer Sports Direct will enter the FTSE 100 as part of the latest reshuffle of the 100 biggest companies on the London Stock Exchange.