While earning his masters, Beloussov co-founded his first business, Unium (Phystech College), which provided science students with course materials. In 1992, he began working at a Russian computer company called Sunrise. Beloussov expanded the company's operations to 10 subsidiaries, becoming one of the largest PC retailers in Russia by the time he left in 1994. After leaving Sunrise, Beloussov founded and co-owned two companies, Rolsen Electronics, which has become one the largest consumer electronics manufacturers in Russia, and Solomon Software SEA, a distributor and developer arm of mid-market ERP vendor Solomon Software in South-East Asia. Solomon Software was later acquired by Microsoft and is now known as Microsoft Dynamics SL.
In 2000, Beloussov founded SWsoft, a privately held server automation and virtualization software company and the then-parent company of Parallels, Inc. and Acronis Inc.
In 2001, Beloussov founded Acronis as a storage management business unit of SWsoft. In 2003, Acronis was re-organized as a separate entity focused on backup and data protection software. Acronis employs over 700 worldwide and its products are sold in 15 languages around the world.
Beloussov has served on the Board of Directors since 2002. From 2007 to 2011, he turned his focus on Parallels, acting as CEO of the company. During this time he also founded a pair of venture capital funds, Runa Captical and QWave Capital. He returned as CEO of Acronis in May 2013, replacing former CEO Alex Pinchev.
Parallels, Inc. was initially a server automation and virtualization software unit of SWsoft before it was spun off into as a separate entity and maintained its own distinct branding. In December 2007, SWsoft announced its plans to change its name to Parallels and ship both companies' products under the Parallels name. The merger was formalized in January 2008. From 2007 to 2013, Beloussov led the company as CEO, while remaining on the board of directors at Acronis.
Beloussov stepped down as CEO and serves as the executive chairman of the board and chief architect of Parallels, Inc. The company has more than 900 employees across offices in North America, Europe, Australia and Asia and as of 2012 it had 5,000 customers and partners worldwide. Odin Automation, a service automation platform company owned by Parallels and founded by Beloussov, was sold to Ingram Micro in December 2015.
In August 2010, Beloussov co-founded Runa Capital with Dmitry Chikhachev and Ilya Zubarev. The $135 million technology venture capital firm that was created "to seek growth opportunities in the rapidly growing areas of the tech sector, with specific focus on cloud computing and other hosted services, virtualization and mobile applications." Beloussov and Zubarev are senior partners at the investment firm. Since 2010, Runa Capital has invested in over 30 companies with a combined $10 billion in assets. Runa Capital's largest investment was a $10 million Series C funding round of Acumatica on November 18, 2013.