Vallance gained entry to the qualifying rounds of the 2017 World Snooker Championship as one of 16 amateur players, who achieved success through the WPBSA qualifying criteria. He qualified as one of 8 Home Nations NGB qualifiers. Vallance would go on to play Sam Baird in the first round of qualifying losing 10–2. In May 2017, Vallance entered Q School, reaching the Last 16 of Q School 2017 – Event 1 before narrowly losing out to Sean O'Sullivan in a deciding frame. Later on that month Vallance won the 2017 Scottish Amateur Championship in 2017, defeating his compatriot Craig MacGillivray 7–6. Vallance has appeared in three further Scottish Amateur Championship finals, losing out in 2009, 2011 and 2018. After winning the 2017 Scottish Amateur Championship, Vallance was invited to take part in the 2017 Scottish Open. Vallance won a pre-qualifying match against Robert Carlisle 4–3. He would then go on to play Ashley Hugill in a first round match in which he was defeated 4–3.