The 22-year-old has been the form outside-half in Wales over the course of the last few months, playing a pivotal role in the Ospreys' march to the RaboDirect Pro12 title.
Biggar started today's 30-21 Millennium Stadium victory over the Barbarians before leaving the field during the second half with what appeared to be a shoulder injury.
But Howley revealed that Biggar's appearance against the Baa-Baas had not even amounted to an audition to provide back-up for Wales' current first-choice number 10 Rhys Priestland, as the player had been informed in midweek that he would not be aboard Monday's flight to Australia for the three-Test series.
The other four players dropped from Howley's original squad are centre Adam Warren, prop Ryan Bevington, wing Will Harries and flanker Martyn Williams, who won his 100th and final cap for his country as a second-half replacement in Cardiff.
With Biggar dropped, James Hook will now compete with Priestland for a starting role down under, and it was the Perpignan man's ability to also play at centre and full-back which proved pivotal in Howley's final selection.
Howley said: "Having spoken to Dan throughout the week we have been mindful of the motivation for the Baa-Baas game as well as the travel logistics for going to Australia.
"We spoke to some of the senior players in terms of guidance of when you actually tell a player he is not going on tour.
"Is it now on the Saturday after the emotion of a Test match or on the Tuesday or Wednesday when they will have time to reflect as obviously it is a huge disappointment?
"Those five players have been spoken to and we have gone through the reasons why they have not been selected.
"Dan has been one of the form players in the RaboDirect Pro12. He has been in our environment over the last year and for longer.
"But James Hook, in terms of the two 10s and the schedule we have got, can play, 10, 12, 13 and 15 and when you are going on a tour of the magnitude of going to the other side of the world to Australia you need flexibility of selection.
"It is no reflection on Dan's form. Dan over the last four months has played particularly well for the Ospreys.
"We have spoken to him about his game management but sometimes it is a numbers game and it is about flexibility when it comes to selecting a squad to go to Australia."
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
A cool looking all black rugby cleat with the high performance adidas is known for. Get in the Gear!
Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.