According to http://malsup.com/jquery/form/#validation you can use the beforeSubmit option to provide a callback that returns true or false.
In this callback simply use the .valid() plugin method described here http://jqueryvalidation.org/valid
$(document).ready(function() {
// jQuery Validation Plugin
$("#myForm1").validate();
// jQuery form Plugin
var options = {
target: '#output1', // target element(s) to be updated with server response
beforeSubmit: validate, // pre-submit callback
success: showResponse // post-submit callback
};
// bind form using 'ajaxForm'
$('#myForm1').ajaxForm(options);
});
// Return validation status from jQuery validate plugin.
function validate(formData, jqForm, options) {
return $('#myForm1').valid();
}