Life on Venus, Past Present and Future..
It's pretty convincing that life does not currently exist on Venus. What about the past? What about the possibility of Terra Forming Venus for future life?
The Sun had 66% its current flux when the Solar System was first created. 4 billion years ago Venus would have been heated about the same as Earth is today. Venus almost certainly had liquid water on its surface, which may have allowed for the development of life. Mars may also have harbored life early on, since we see early evidence for running water (as well as possible more recent evidence).
So, 4 Billion years ago, it's possible that life existed on Venus, Earth AND Mars, all at once, evolving simultaneously and independently, or perhaps on just one of the planets which proceeded to infect the other two via meteorites. See further discussions on the possibility of Venusian Life here.
Unfortunately, in the case of Venus, the entire surface has been recently replaced. This makes it virtually impossible to search the rocks for fossil or chemical evidence for early life. It seems unlikely we will ever know about past life on Venus--unless there is a meteorite out there with evidence saved in it!
Terra Forming Venus
It may seem a daunting task, but terra forming Venus might not be
entirely impossible. This is for the most part due to the very powerful
instability that exist, involving the atmosphere, surface rocks and volcanism.