This PowerShell script is using Google BigQuery REST API to run a query and creates a result set using returned schema for field names and types

RunGBigQuery.ps1

$project = "your-gcp-project"
$accesstoken = gcloud auth print-access-token # Lazy way. Can also get access token using service account and 2LO - ref. https://gist.github.com/SP3269/da43b00692de5b3f591b3068d76df577

# Using Google BigQuery REST API per https://cloud.google.com/bigquery/docs/reference/rest/v2/jobs/query

# Example query using public dataset available to anyone in BQ
$query = 'SELECT * FROM `bigquery-public-data.san_francisco_trees.street_trees` WHERE plant_date >= "1969-01-01 00:00:00 UTC" AND plant_date < "1970-01-01 00:00:00 UTC"'

$body = @{
    useLegacySql = "false"
    query = $query
}

$request = @{
    Uri = "https://www.googleapis.com/bigquery/v2/projects/$project/queries"
    Method = "POST"
    Headers = @{Authorization = "Bearer $accesstoken"; "Content-Type" = "application/json"; Accept = "application/json"}
    Body = $body | ConvertTo-Json
}

$res = Invoke-RestMethod @request -Verbose

# Column names in $res.schema.fields.name
# Row values are in $res.rows[0].f.v

# TODO: types. Types can be STRING, FLOAT - need conversion of value before Add-Member

$epoch = Get-Date "1970-01-01T00:00:00Z"

$fieldcount = $res.schema.fields.count
$columnnames = $res.schema.fields.name
$columntypes = $res.schema.fields.type
$rowcount = $res.rows.count

$data = for ($j=0; $j -lt $rowcount; $j++) {
    $row = $res.rows[$j].f.v
    $entry = New-Object PSCustomObject
    for ($i=0; $i -lt $fieldcount; $i++) {
        $fieldvalue = $row[$i]
        if ($null -eq $fieldvalue) {
            $entry | Add-Member -NotePropertyMembers @{$columnnames[$i]=$null}
        }
        else {
            switch ($columntypes[$i]) {
                "FLOAT" { $entry | Add-Member -NotePropertyMembers @{$columnnames[$i]=[float]$fieldvalue} }
                "INTEGER" { $entry | Add-Member -NotePropertyMembers @{$columnnames[$i]=[int]$fieldvalue} }
                "TIMESTAMP" { $entry | Add-Member -NotePropertyMembers @{$columnnames[$i]=$epoch.AddSeconds($fieldvalue)} }
                Default { $entry | Add-Member -NotePropertyMembers @{$columnnames[$i]=$fieldvalue} } # String as the default
            }
        }
    }
    $entry
}

$data