DST has agreed to pay $14.77 per share, giving Facebook's common stock a value of about $6.5bn.
Mark Zuckerberg, CEO of Facebook, said in a statement: "This is recognition of Facebook's growth and progress towards making the world more open and connected."
DST indicated it was planning to offer to purchase at least $100m of Facebook's common stock in May after , valuing it at $10bn.
The deal today carries a valuation of $6.5bn because it involves Facebook's common shares, which have fewer privileges and guarantees than preferred stock.
If enough employees take DST up on its offer, it will give the investor a further 1.54% stake in Facebook, taking its total ownership to 3.5%.
Based in London and Moscow, DST is an investor in a number of internet companies, holding significant interests in Russia and Eastern Europe, such as Mail.ru, the leading Russian-language website.
Earlier this month, board member Marc Andreessen said this year and will likely be posting billions of dollars in revenue in five years.
Andreessen, who founded Netscape and has just launched a venture capital fund with another former Netscape executive Ben Horowitz, said it was a mistake for Facebook shareholders to be selling their stock now.