Kaspars started playing basketball in his hometown Ogre. Later he played for Skonto Riga, debuting in 2002-2003 season. His role increased in 2003-2004, when he averaged 7.3 points and 3.3 rebounds for Skonto in the LBL and 7.3 points and 3.0 rebounds in the FIBA Europe League, now known as the FIBA EuroCup. In both of those seasons Bērziņš played together with Andris Biedriņš. In 2004 both of them left Skonto. Biedriņš was drafted in the NBA by Golden State Warriors, while Bērziņš moved to Spain where he joined Unicaja Málaga. He briefly played for Unicaja's first team, where he competed in one game in the ACB league, scoring two points, but most of the season spent with the junior team in the EBA, Spain's second division. For the 2004-2005 season Bērziņš moved back to Latvia, playing big role for Skonto. Averaged 13.0 points, 6.1 rebounds and 1.0 blocks in 21.3 minutes in the LBL and 14.8 points and 8.3 rebounds in four EuroCup Challenge games. After Skonto disappeared Bērziņš moved to ASK Rīga, where he played in 2005-2006 season. In the following off-season Bērziņš signed with Barons LMT, where he played next three seasons and won his first Latvian league title in 2008. During that season Bērziņš won in FIBA EuroCup as well. 2008-2009 was best season with Barons, when he was team's top inside presence for most of the season, averaging 14.0 points, 8.rebounds and 1.9 blocks in 28 games of domestic competition. In July 2009 Bērziņš participated in NBA Summer League, playing for Phoenix Suns. After playing for Phoenix in Summer League Bērziņš signed contract with Spain's ACB League clubFuenlabrada. Later he also played for Cáceres Ciudad del Baloncesto, but in July 2010 signed two-year contract with VEF Rīga. He re-signed with VEF Rīga for three more years in 2012. In February 2014, he comes back to Spain and signed with Río Natura Monbús for the rest of the 2013–14 ACB season. On August 21, 2014, he signed with Russian club Krasnye Krylia for the 2014–15 season. On June 16, 2015, he signed with Nizhny Novgorod. In January 2016, he left Nizhny and signed with Zenit Saint Petersburg for the rest of the season. The 2016–17 season Bērziņš started with Latvian club Ogre/Kumho Tyre but in January 2017, he returned to Russia and signed with Lokomotiv Kuban for the rest of the season.
