You can do this using Google's BigQuery .Net client library.
Please refer their documentation : Google.Cloud.BigQuery.V2
Before proceed you have to go to APIs & Services, then search for "BigQuery API" and enable it.
Then you have to install their client library using Nuget Package manager.
Install-Package Google.Cloud.BigQuery.V2
Then you need to download Service Account key for the authentication.
For that you have to create a service account, then create a new key for that service account as json. Then you have to download that json file.
Then you can connect with your BigQuery as below:
static void Main(string[] args)
{
string keyPath = "path_to_downloaded_json_file";
var credential = GoogleCredential.FromFile(keyPath);
BigQueryClient client = BigQueryClient.Create("your_project_name", credential);
BigQueryTable table = client.GetDataset("your_dataset_name").GetTable("your_data_table_name");
string sql = $"SELECT your_column AS foo, your_other_column AS bar FROM {table}";
BigQueryParameter[] parameters = null;
BigQueryResults results = client.ExecuteQuery(sql, parameters);
foreach (BigQueryRow row in results)
{
Console.WriteLine($"{row["foo"]}: {row["bar"]}");
}
}