On June 6, 2011, at the Apple Worldwide Developers Conference, it was announced that the official release for Lion would be in July 2011. The specific release date of July 20 was not confirmed until the day before, July 19, by Apple CFO, Peter Oppenheimer, as part of Apple's 2011 third-quarter earnings announcement.

Apple did not initially announce any physical media distribution for Lion, such as a set of CD-ROMs or a DVD-ROM as used for past releases. Instead, the operating system was said to be available exclusively as a download from the Mac App Store for US$29.99. The only prior version of OS X that supports the Mac App Store is Snow Leopard, which implied that any machines that support Lion currently running Tiger or Leopard rewould first have to be upgraded to Snow Leopard, as opposed to allowing a direct upgrade to Lion.

Apple later announced two alternative distribution mechanisms for the benefit of users without broadband Internet access: in-store downloads at retail Apple Stores, and a USB flash drive containing the OS, priced at US$69, available through the online Apple Store beginning in August. On August 4, 2011, Apple started to take orders for OS X Lion's USB installation flash drives for $69.99.

The Server portion of Lion is available as a separate download from the Mac App Store for US$49.99, which is in addition to the purchase price of Lion itself. In July 2012, Lion was removed from the Mac App Store and retail Apple stores following the release of OS X Mountain Lion. Following the removal of Lion from the Mac App Store, customers could still purchase Lion by phone at the reduced price of $20. In October 2013, Lion was returned to the Apple Store website concurrently with Mountain Lion following the release of OS X Mavericks for the convenience of users who cannot run Mavericks on older Mac models.

The first developer preview of Lion added TRIM support for Solid-state drives (SSD) shipped with Macs, which is also included in the latest version of Snow Leopard (10.6.8) shipping with MacBook Pros before July 20, 2011. Other SSDs have built-in TRIM-like optimization, while yet others require OS patching.

System requirements

• x86-64 CPU (64-bit Macs, with an Intel Core 2 Duo, Intel Core i5, Intel Core i7, or Xeon processor.)
• At least 2 GB of memory
• Mac OS X 10.6.6 or later (Mac OS X 10.6.8 is recommended)
• 7 GB of available space
• AirDrop is supported on the following Mac models: iMac (early 2009 or newer), MacBook (late 2008 or newer), MacBook Air (late 2010 or newer), MacBook Pro (late 2008 or newer), Mac Mini (mid 2010 or newer), and Mac Pro (early 2009 with AirPort Extreme card and mid 2010 or newer).

Some new features were announced at the "Back to the Mac" keynote in October 2010, and the Apple website was updated in February 2011 with more details. Other features were announced at the WWDC 2011 keynote or on Apple's OS X Lion Web site after the keynote. Apple stated that there were over 250 new or changed features in Lion, including:

• Address Book uses an iPad-like user interface. It also includes improved Yahoo support and FaceTime calling.
• AirDrop – Lion-to-Lion direct file sharing via Wi-Fi Direct, with no wireless access point required.
• Address space layout randomization – Address space layout randomization (ASLR), a security technique that puts important data in unpredictable locations, making it harder to target known weaknesses, is available for 32-bit applications, and "has been improved for all applications", in Lion.
• Apple Push Notification Service – Send over-the-air alerts, such as news updates or social networking status changes, using Apple's Push Notification service to applications that support APNS. APNS allows OS X Lion and iOS clients to receive push changes to items such as mail, calendar and contacts from a configured OS X Lion Server.
• Auto-correction behaves much like on iOS devices, displaying an iOS-like popup box.
• Auto Save – As in iOS, documents in applications written to use Auto Save are saved automatically so users do not have to worry about manually managing their documents. The Auto Save feature significantly alters traditional workflow patterns and is a controversial addition to the system.
• Emoji support – Apple has added a new Emoji font commonly used in chat to express ideograms.
• Exposé in the Dock, a way of activating Exposé for a single application from the Dock, a feature added in Mac OS X 10.6, is altered. One must double-tap with two fingers on a dock icon to initiate single-application Exposé, or simply right-click or control-click and select Show All Windows.
• FaceTime comes bundled with Lion.
• FileVault offers full disk encryption and added security with XTS-AES 128 data encryption. Support for FileVault on external hard drives has also been added.
• Finder improvements – Finder search allows multiple search criteria to be specified without creating a smart folder, Finder search offers suggestions, files can be grouped by various attributes, and one can merge files under two folders with the same name – a prompt appears asking to replace or keep both files. The navigation sidebar lost the ability to show the specific icon of a map or volume (by default; there is a hack to still add the old ability), instead it shows a grey standard map icon.
• Font Book 3 – Font Book 3 provides more flexible displays of character glyphs supplied by a particular font face. Duplicate font files are flagged with a warning icon, and can be fixed automatically or resolved manually.
• Full-screen apps – Native, system-wide support for full-screen applications running in their own space. Supporting applications display a new button at the top right of application window, this button opens applications in full-screen mode. However, full screen mode is not supported for dual screen setups.
• High-quality multilingual speech voices – users can download new high-quality voices in more than forty languages and dialects.
• iCal has an updated user interface, an annual view, and support for a full-screen view.
• iChat has support for logging into Yahoo! Messenger. Users can audio- and video-chat with other iChat users using their Yahoo! accounts.
• Languages/Localization – Arabic, Czech, Turkish and Hungarian are added as full system languages, to make the total number of twenty-two languages available in Mac OS X.
• Launchpad – An application launcher that displays an iOS-like icon grid of installed applications. It features the ability to make multiple pages and group apps into folders that function the same as folders in iOS.
• Mac App Store – receives support for in app purchases as with iOS, and alters the update mechanism to no longer create a separate copy of the app, improving performance.
• Mail 5 – Uses an iPad-like user interface, has a fullscreen-optimized view, uses chronological "Conversations" to organize messages, and supports Exchange 2010 (but not through the Exchange ActiveSync protocol, as iOS).
• Mission Control replaces the "All windows" Exposé feature. It gives an overview of all running applications just like "All windows" but groups windows from the same application. At the top of the screen it gives quick access to the Dashboard, Spaces, and running full-screen applications.
• Multi-touch gestures – Similar to iOS, additional gestures performed using a multi-touch input device (e.g. Magic Mouse, Magic Trackpad) allow the user to scroll, swipe to different pages, and enter Mission Control. While this is not the first official multi-touch support for Mac OS X, it has been expanded; other frameworks, such as Lux, have already created multi-touch support.
• Multi-User Screen Sharing – The built-in Screen Sharing feature allows remote users to log into a separate user account from the one that is currently logged in. While one user is logged into a machine, a second user can log into the same machine remotely, seeing their own desktop and user environment.
• Preview gains several features, including full-screen support and the ability to sign a document just by holding a signed piece of paper up to the camera.
• Profile Manager provides several features, including push notification-based management of OS X Lion and above.
• QuickTime reincorporates some features from QuickTime Pro. New features cited include Copy/Paste, Insert Clip, Crop Video, Rotate Video, Resize, Trim, and more Export options.
• Recovery Partition – Apple has introduced a recovery partition that includes utilities generally found on the OS X discs. This partition enables the user to restore their computer to its original factory state without the original installer media such as a flash drive. If the partition were to become damaged or otherwise not available, such as with a new drive, a new copy of OS X Lion can be installed over the internet.
• Resume – Applications resume in the same state when re-opened as already seen in iOS.
• Safari – With full-screen mode and the new WebKit2 layout engine.
• System Information – This feature is a re-design of System Profiler, which has been completely altered with new views which display graphical information on displays, storage devices, memory usage along with other hardware information. The previous layout remains available by clicking "System Report". Early builds of Lion also used System Information as a replacement for "About This Mac", although the final release reinstated the version of this dialog box found in Snow Leopard.
• Terminal has extra features, including full screen mode.
• TextEdit gains a new graphical toolbar with font selection and text highlighting. The new TextEdit also supports Apple's new automatic file saving and versions technologies.
• Versions – Time Machine-like saving and browsing of past versions of documents for applications written to use Versions.
• Vertical text – Lion supports vertical layouts for East Asian languages.

The complete list was on Apple's website but has since been taken down; it can now be found on the Internet Archive. The developer release notes may also be of interest.