Use Putty with Existing SSH Keys on Windows

How to convert an existing Open SSH private key file to a Putty Private Key file (ppk) for use with Putty on Windows.  

Putty uses a different SSH key file format from Open SSH, Putty Private Key file (ppk). To use a private key created using OpenSSH with Putty, you will first need to convert it to a .ppk file using PuTTYgen.

Install PuTTY and PuTTYgen

Download PuTTY: latest release
https://www.chiark.greenend.org.uk/~sgtatham/putty/latest.html

Convert existing private key

Convert an existing private key using PuTTYgen

Open PuTTYgen
Select the key type e.g. ECDSA
Conversions - Import Key

Browse for your Open SSH private key file and enter the passphrase when prompted.

Save the private key to C:\Users\Username\.ssh as a Putty private key .ppk file

Save private key

Connect using private key

Connect to server using Putty private key

Open Putty

Session
Enter host name or IP address
Connection type SSH, port 22

Connections - SSH - Auth
Browse for Putty private key file .ppk

You can also save the login username, which means you will only get prompted for the private key passphrase when connecting. The username will be automatically entered.

Connection - Data - Auto-login username

Click open to connect to the server

You will be prompted for the private key passphrase when connecting

Save Session

Enter a name for the session e.g. server-name, and save the settings.
You can load the session settings next time you open Putty.