You can leverage the GitHub Events API to perform such task and retrieve a JSON formatted response.

The Events API is a read-only interface to all the event types that power the various activity streams on GitHub.

• syntax: GET /users/:user/events
• example: https://api.github.com/users/mojombo/events

An alternative way is to subscribe to the public RSS feed of a user. For instance, Mojombo's public feed Url would be

• https://github.com/mojombo.atom

Also If you want to view Full activities performed by all contributors ,you can also go to

If Private https://github.com/orgs/YOURORGANISATION/dashboard

If Public https://github.com/REPOSITORYOWNER?tab=activity

Most contribution data can be fetched using Github GraphQL API - https://developer.github.com/v4/

I was using this method for doing a widget that shows the last user contributions list. And it works well and offers many of filtering/grouping opportunities

a.e you can get contribs count by day:

{
  user(login: "orn0t") {
    contributionsCollection {
      contributionCalendar {
        totalContributions
        weeks {
          contributionDays {
            contributionCount
            weekday
            date
          }
        }
      }
    }
  }
}

If you're looking for working code examples:

you can view my project on Github - https://github.com/orn0t/gh-contrib-widget.