Vejonis was born near Pskov in Russia while his father was serving in the military, just across the border from his Latvian homeland which at that time in 1966 was occupied by the Soviet Union.
He trained as a biologist at the University of Latvia in 1989 while teaching biology in the small central Latvian town of Madona and also studied in Estonia and Finland, specialising in environmental engineering.
In 2002 he was appointed by reforming Prime Minister Einars Repse as Environment Minister, without being elected to parliament, while serving as a local councillor in Madona.
In 2006 Vejonis was elected to parliament for the Greens and Farmers Alliance grouping which includes the Latvian Green Party of which he is a member.
He is one of the longest-serving of all Latvia's current crop of politicians despite his relatively young age, keeping the environment minister's portfolio through successive coalitions until 2011 when he resumed duties as a regular member of parliament, sitting on foreign policy and national security committees.
That led to a recall to front-line duty in January 2014 when Prime Minister Laimdota Straujuma appointed him Defence Minister. It was widely speculated at the time that he might be too weak, particularly in comparison with his hawkish predecessor Artis Pabriks, however Vejonis has managed to disprove the doubters by taking a tough stance on Russian aggression and even blasting Greens and Farmers Alliance kingpin Aivars Lembergs as a “threat to national security” after he described NATO troops in Latvia as “occupiers.”
In May he told the Diena newspaper his belief in environmentalism grew not only from a general interest in nature but when he learned that his grandfather had been blinded by the use of dangerous chemicals on a Soviet collective farm.
“The destruction of forests can be likened tot he demolition of churches,” he said in 2010.
However, despite being a Green Party member for 25 years, Iveta Kazoka of the Providus centre for policy analysis says Latvia's greens do not fit the usual EU pattern of left-leaning social democracy and strong environmental commitment, a pattern established in 2004 when Vejonis' part colleague Indulis Emsis became the EU's first 'green' Prime Minister.
“It seems to me he's in the Green Party as a matter of political convenience as a career politician rather than principle or strong ideological convictions. He's quite fond of the environment but I would struggle to name anyone in the Latvian Green Party who would fit the profile of a regular European Green Party member,” Kazoka told LSM.
“He's quite understated as a politician. As a President he would not be as visible as leaders of some other states, but he definitely represents progress when compared to [current president] Andris Berzins. People don't really have bad things to say about Vejonis, but nor will you meet people who praise him as a charismatic politician. He was elected on the principle of the lesser of two evils rather than being the best person Latvia's ever seen.”
As well as his native Latvian, Vejonis speaks fluent Russian and English. He is married with two children and lists his religious views as “pagan” on his Facebook page.