Pricing will start at US$349 ($425).
The iPhone 6 and 6 Plus are larger and slimmer than their predecessors. The 6 will have a 12cm screen and will retail from $999 for 16GB, while the 6 Plus will have a 14cm screen and will start at $1149 for 16GB.
Apple says the new phones will be faster and have better battery life than previous versions.
The company is also introducing Apple Pay, a system for using the iPhone and Apple Watch to make credit card payments at retail stores.
Like other smart watches, such as Motorola's Moto 360 and Samsung's Gear S, the Apple Watch will enable its owner to do more than just tell the time, which it will do to within 50 milliseconds.
There's a walkie talkie function, users can read texts, emails and screen calls from their phone, there's a calendar, and it works as a controller for iTunes and Apple TV.
Navigation is done through the watch's side dial, which doubles as the home button, a second button below, and a touch screen made of crystal sapphire, a transparent material that Apple claims is the hardest after diamond.
The watch and the iPhone 6 were released to great fanfare at the Flint Centre for the Performing Arts in Cupertino, California, the same venue where Apple founder Steve Jobs unveiled the industry-shifting Mac computer 25 years ago.
Daven Naidu is champing at the bit to get his hands on an Apple Watch. So keen that when his watch was stolen recently, he didn't replace it.
"I want one now. It's not just another watch," he said. "Apple has put a lot of thought into its functionality and usability - it's not just another gadget."
The managing director of Apple retailer Yoobee said the product would open a world of opportunities for developers.
A smart watch was not as revolutionary as the iPad but "I think Apple has again created a new category of product".
Battery life was not mentioned but the device charges from a magnet that attaches to its back.
