How to Incorporate Swift Package Manager to an Existing Xcode Project?

The generated Xcode project from SPM is different from your app's Xcode project/workspace.

You should generate that Xcode project in another directory eg. "Dependencies".

Then drag it into your app's, and add the linked framework. I have written a full step-by-step.

Steps to achieve Swift Package Manager and XCode integration in 2019:

1) Create Dependencies.swift file /yourproject/Dependencies/Sources/Dependencies.swift

(empty file)

2) Create macos.xcconfig file /yourproject/Dependencies/Sources/macos.xcconfig

MACOSX_DEPLOYMENT_TARGET = 10.14

3) Create Package.swift file /yourproject/Dependencies/Package.swift

// swift-tools-version:4.2
import PackageDescription

let package = Package(
    name: "Dependencies",
    products: [
        .library(name: "Dependencies", type: .static, targets: ["Dependencies"])
    ],
    dependencies: [
        .package(url: "https://github.com/YourDependency/here.git", .upToNextMinor(from: "0.1.0"))
    ],
    targets: [
        .target(name: "Dependencies", dependencies: ["YourDependency"])
    ]
)

4) Generate Dependencies.xcodeproj and drag-and-drop into your existing project

swift package generate-xcodeproj --xcconfig-overrides Sources/macos.xcconfig

5) Import your dependency

import YourDependency

This is enough to make it work but you can make your life a bit easier with a few extra steps.

Additional (optional) steps:

6) Create ios.xcconfig file /yourproject/Dependencies/Sources/ios.xcconfig

SDKROOT = iphoneos
SUPPORTED_PLATFORMS = iphonesimulator iphoneos
IPHONEOS_DEPLOYMENT_TARGET = 10.0

ARCHS = $(ARCHS_STANDARD)
VALID_ARCHS = $(ARCHS_STANDARD)

VALIDATE_PRODUCT = YES
LD_RUNPATH_SEARCH_PATHS = $(inherited) @executable_path/Frameworks
TARGETED_DEVICE_FAMILY = 1, 2

7) Add Pre-build action to your main project's iOS and macOS Schemes

iOS

echo "Building SPM Dependencies"
BASE_DIR="${PROJECT_DIR}/Dependencies"
cd ${BASE_DIR}

rm -fr Dependencies.xcodeproj
swift package update
swift package generate-xcodeproj --xcconfig-overrides Sources/ios.xcconfig

sleep 3

until [ -d "Dependencies.xcodeproj" ]
do
echo "File not found"
sleep 0.1
done
echo "File found"
exit

macOS

echo "Building SPM Dependencies"
BASE_DIR="${PROJECT_DIR}/Dependencies"
cd ${BASE_DIR}

rm -fr Dependencies.xcodeproj
swift package update
swift package generate-xcodeproj --xcconfig-overrides Sources/macos.xcconfig

sleep 3

until [ -d "Dependencies.xcodeproj" ]
do
echo "File not found"
sleep 0.1
done
echo "File found"
exit

8) Run your project and enjoy :)

All the answers here are real old and outdated so I decided to add some modern context in case anyone comes across this like I did.

Apple has done some seriously awesome upgrades to Xcode to natively support Swift Package Manager out of the box. The following image shows my local package (that I build and maintain) incorporated with the demo project included in the git repo. Navigating to this page (3) and clicking the + button (4) will open a dialogue to add remote packages from git repositories. This can be done with any .xcproj file.

Apple also has a lot of wonderful documentation on how to build and support Swift Packages yourself, or how to incorporate them into your app.

It's very good practice to organize your code into local package dependancies per the documentation:

Swift packages are a convenient and lightweight solution for creating a modular app architecture and reusing code across your apps or with other developers. Over time, you may want to develop your published Swift package in tandem with your app, or create a sample app to showcase its features. To develop a Swift package in tandem with an app, you can leverage the behavior whereby a local package overrides a package dependency with the same name:

1. Add the Swift package to your app as a package dependency instead of a local package, as described in Editing a Package Dependency as a Local Package.

2. Develop your app and your Swift package in tandem, and push changes to their repositories.

3. If you release a new version of your Swift package or want to stop using the local package, remove it from the project to use the package dependency again.

See Apple's official Swift Package Manager Documentation for more up-to-date information.

Many loves! <3