The 27 year-old, who pushed ahead with the acquisition with little input from his board of directors, told investors in New York that Instagram's thriving user base influenced the move.
Zuckerberg explained that Instagram's user data hit a "tipping point", from which it is expected to skyrocket. The interest of other potential buyers, including Twitter, forced the executive's hand.
Facebook acquired Instagram, which has more than 40 million users, for $1bn (£629m) last month. The social network has pledged to keep the photo-sharing service running as a separate operation.
Zuckerberg also outlined plans to launch Facebook over in China, a country which blocks access to the service due to its censorship laws. Facebook executives are hoping to hold a meeting with the Chinese government with a view to expanding the service to the region.
Facebook set its share prices ahead of its forthcoming initial public offering, valuing each between $28 (£17.30) and $35 (£21.60), which places the company between $85bn and $95bn (£52bn-£59bn).