Not able to upload file using Ajax.BeginForm() asynchronously

You cannot upload files using AJAX. This is not supported. If you want to do that you could either use some file upload plugin such as Uploadify or Blueimp File Upload or use the HTML 5 File API if the client browser supports it.

You can do this without additional libraries.

I came across this little hack, which resolves it nicely

window.addEventListener("submit", function (e) {
    var form = e.target;
    if (form.getAttribute("enctype") === "multipart/form-data") {
        if (form.dataset.ajax) {
            e.preventDefault();
            e.stopImmediatePropagation();
            var xhr = new XMLHttpRequest();
            xhr.open(form.method, form.action);
            xhr.onreadystatechange = function () {
                if (xhr.readyState == 4 && xhr.status == 200) {
                    if (form.dataset.ajaxUpdate) {
                        var updateTarget = document.querySelector(form.dataset.ajaxUpdate);
                        if (updateTarget) {
                            updateTarget.innerHTML = xhr.responseText;
                        } 
                    }
                }
            };
            xhr.send(new FormData(form));
        }
    }
}, true);

Found http://www.acnenomor.com/1762557p1/c-mvc3-ajaxbeginform-to-upload-file-not-working