There are several add-ons out there that you can use to sync your Google Calendar with Microsoft Outlook. But, you can also view your Google Calendar in Outlook without using an add-on since both calendar apps support iCal.
Despite its name, the iCal we mean here is not something related to Apple. It is an open standard to exchange information between internet-based calendar apps. In order to view a calendar from a certain calendar app in another calendar app, you need the link of the associated calendar you want to access.
In addition to Outlook, you can also view your Google Calendar in other apps that support iCal.
How to view Google Calendar in Outlook
You need the URL of the calendar on Google Calendar that you want to view from Outlook. The first thing you need to is log in to Google Calendar with your Google account. Once logged in, hover your mouse over a calendar on the left panel and click the three-dot icon and select Settings and sharing.

Next, scroll down to the Secret address in iCal format section and copy the URL.

Once you got the URL, launch Outlook and go to the calendar tab by clicking its icon on the navigation menu on the bottom side. On the calendar tab, right-click a calendar group (you can select any group) on the left panel and select Add Calendar -> From Internet.

In order to make your calendars be more organized, it’s a great idea to create a new calendar group. To do so, you can click Calendar Group on the toolbar.
Paste the URL you copied from Google Calendar on the appearing popup and click the OK button.

Wait a moment and you will see the following confirmation dialog. Click Yes.

That’s it. You can now view your Google Calendar on your Outlook.

You can view your Google Calendar in the daily mode, week, or moth. If you are no longer need to view your Google Calendar, you simply remove it by right-clicking the calendar on the left panel and select Delete Calendar.

One thing you need to note here is that you are not fully integrating your Google Calendar with Outlook. You still need to manage your schedules via Google Calendar. You can’t add or delete schedules via Outlook. However, all changes you made on Google Calendar will be applied to Outlook as well.