user3495: Wolfgang Unzicker was a German GM, rated about 2550 and worked as a judge. In the sense of holding down a job while playing, he was an "amateur" player. 
So was Unzicker, a GM in the 70's, the last amateur GM?  

user15223: There are plenty of GMs that do not play professionally, e.g. GM Luke McShane is a financial trader, GM Hou Yifan is a Rhodes scholar. So if your definition of "amateur" is holding down a job while playing occasionally, Wolfgang Unzicker certainly was not the last amateur GM.

user9645: The economist Ken Rogoff (b. 1953) achieved the GM title in 1978, but was never a "professional" chess player. Rogoff is currently a professor of economics at Harvard University.

user4418: 
So in the sense of holding down a job while playing he was an
  "amateur" player.
So was Unzicker, a GM in the 70's, the last amateur GM?

No. Here are 4 current British "amateur" grandmasters.

English GM Matthew Turner is a teacher at Millfield School in Somerset.   
English GM Matthew Sadler is a computer consultant in the Netherlands.   
English GM Luke McShane (currently on 4/7 in the Netanya Masters) is a financial trader in London   
Scottish GM Dr. Jonathan Rowson is Director of the Social Brain Centre at the Royal Society of Arts in London   


3495: <p><a href="https://en.wikipedia.org/wiki/Wolfgang_Unzicker" rel="noreferrer">Wolfgang Unzicker</a> was a German GM, rated about 2550 and worked as a judge. In the sense of holding down a job while playing, he was an "amateur" player. </p>

<p>So was Unzicker, a GM in the 70's, the last amateur GM?  </p>
 15223: <p>There are plenty of GMs that do not play professionally, e.g. GM <a href="https://www.theguardian.com/sport/2017/jul/14/luke-mcshane-shares-third-consecutive-title" rel="noreferrer">Luke McShane is a financial trader</a>, GM <a href="https://www.bsg.ox.ac.uk/people/yifan-hou" rel="noreferrer">Hou Yifan is a Rhodes scholar</a>. So if your definition of "amateur" is holding down a job while playing occasionally, Wolfgang Unzicker certainly was not the last amateur GM.</p>
 9645: <p>The economist <a href="https://en.wikipedia.org/wiki/Kenneth_Rogoff#Chess" rel="noreferrer">Ken Rogoff</a> (b. 1953) achieved the GM title in 1978, but was never a "professional" chess player. Rogoff is currently a professor of economics at Harvard University.</p>
 4418: <blockquote>
  <p>So in the sense of holding down a job while playing he was an
  "amateur" player.</p>
  
  <p>So was Unzicker, a GM in the 70's, the last amateur GM?</p>
</blockquote>

<p>No. Here are 4 current British "amateur" grandmasters.</p>

<ul>
<li>English GM Matthew Turner is a teacher at Millfield School in Somerset.   </li>
<li>English GM Matthew Sadler is a computer consultant in the Netherlands.   </li>
<li>English GM Luke McShane (currently on <a href="https://chess24.com/en/watch/live-tournaments/netanya-masters-2019/7/1/1" rel="noreferrer">4/7 in the Netanya Masters</a>) is a financial trader in London   </li>
<li>Scottish GM Dr. Jonathan Rowson is Director of the Social Brain Centre at the Royal Society of Arts in London   </li>
</ul>
