"At this crucial moment for the future of their country, Ukraine's institutions and voters responded to daunting challenges with an election that largely upheld democratic commitments," said Kent Harstedt, head of the OSCE observer mission.
"That response and, in particular, the authorities' determination to enable voting in as many areas of the country as possible, demonstrate a resilience that will help the country overcome its national and international challenges," Harstedt, from the Organisation for Security and Cooperation in Europe, said at a press conference.
Andrej Plenkovic, head of the European Parliament delegation in the observer mission, said Ukrainians had "chosen Europe and peace".
The parties were likely to form a ruling coalition, with Yatsenyuk keeping his premier's post.
The election took place against the backdrop of a bitter dispute with Russia, which seized Ukraine's Crimean province in March, and a war against pro-Russian insurgents in the east of the country.