La réponse la plus votée de @Kelly n'est plus valide, comme le dit @wescpy. Cependant, après le 03/03/2020, cela ne fonctionnera pas du tout car la bibliothèque utilisée utilise Google Sheets v3 API.
  L'API Google Sheets v3 sera fermée le 3 mars 2020
https://developers.google.com/sheets/api/v3
Cela a été annoncé le 10/09/2019 par Google:
https://cloud.google.com/blog/products/g-suite/migrate-your-apps-use-latest-sheets-api
Nouvel exemple de code pour Google Sheets v4 API:
Aller à 
https://developers.google.com/sheets/api/quickstart/dotnet
et générer credentials.json. Ensuite, installez Google.Apis.Sheets.v4NuGet et essayez l'exemple suivant:
Notez que j'ai eu l'erreur Unable to parse range: Class Data!A2:Eavec l'exemple de code mais avec ma feuille de calcul. Changer pour Sheet1!A2:Etravailler cependant puisque ma feuille a été nommée ainsi. Également travaillé avec seulement A2:E.
using Google.Apis.Auth.OAuth2;
using Google.Apis.Sheets.v4;
using Google.Apis.Sheets.v4.Data;
using Google.Apis.Services;
using Google.Apis.Util.Store;
using System;
using System.Collections.Generic;
using System.IO;
using System.Threading;
namespace SheetsQuickstart
{
    class Program
    {
        // If modifying these scopes, delete your previously saved credentials
        // at ~/.credentials/sheets.googleapis.com-dotnet-quickstart.json
        static string[] Scopes = { SheetsService.Scope.SpreadsheetsReadonly };
        static string ApplicationName = "Google Sheets API .NET Quickstart";
        static void Main(string[] args)
        {
            UserCredential credential;
            using (var stream =
                new FileStream("credentials.json", FileMode.Open, FileAccess.Read))
            {
                // The file token.json stores the user's access and refresh tokens, and is created
                // automatically when the authorization flow completes for the first time.
                string credPath = "token.json";
                credential = GoogleWebAuthorizationBroker.AuthorizeAsync(
                    GoogleClientSecrets.Load(stream).Secrets,
                    Scopes,
                    "user",
                    CancellationToken.None,
                    new FileDataStore(credPath, true)).Result;
                Console.WriteLine("Credential file saved to: " + credPath);
            }
            // Create Google Sheets API service.
            var service = new SheetsService(new BaseClientService.Initializer()
            {
                HttpClientInitializer = credential,
                ApplicationName = ApplicationName,
            });
            // Define request parameters.
            String spreadsheetId = "1BxiMVs0XRA5nFMdKvBdBZjgmUUqptlbs74OgvE2upms";
            String range = "Class Data!A2:E";
            SpreadsheetsResource.ValuesResource.GetRequest request =
                    service.Spreadsheets.Values.Get(spreadsheetId, range);
            // Prints the names and majors of students in a sample spreadsheet:
            // https://docs.google.com/spreadsheets/d/1BxiMVs0XRA5nFMdKvBdBZjgmUUqptlbs74OgvE2upms/edit
            ValueRange response = request.Execute();
            IList<IList<Object>> values = response.Values;
            if (values != null && values.Count > 0)
            {
                Console.WriteLine("Name, Major");
                foreach (var row in values)
                {
                    // Print columns A and E, which correspond to indices 0 and 4.
                    Console.WriteLine("{0}, {1}", row[0], row[4]);
                }
            }
            else
            {
                Console.WriteLine("No data found.");
            }
            Console.Read();
        }
    }
}