The toxicity of lead has been known for a long time, and laws regulating the use of lead have been around for at least a few centuries. The ancient Romans were aware of the danger of lead, and knew of illness caused by the fumes from casting lead, and the toxicity of white lead if eaten ("white lead" is a lead carbonate, and is also the form of lead used in lead paints). They did use lead water pipes, but considered clay pipes better for health. Lead-coated cooking pots were used, and these could in some cases have caused lead poisoning. (Why coat cooking pots in lead? Because copper or bronze pots can release toxic copper salts if used to cook acidic foods. In this case, for at least some foods, the risk of lead poisoning might have been lower than the risk of copper poisoning.) The risks of lead in cooking became better known later, and tin replaced lead as the standard coating for copper pots. In some cases, laws regulated the use of lead in the preparation of food and drink. For example, in the early 1700s, Massachusetts banned the use of lead in stills for making rum (because their customers in North Carolina complained about getting lead poisoning from New England rum).

Lead was widely used in paints because white lead is an excellent additive for making white paint more opaque, allowing a thinner (and therefore cheaper) layer of paint to hide the underlying cover. (Why? White lead has a high refractive index, of about 2, and small particles will scatter light effectively. White paint is white for the same reason that snow is white - it scatters incoming light randomly and stops it from getting through the paint.) The risks of lead paint were certainly known in the 19th century - Germany banned the employment of women and children in factories making lead paint (and lead acetate) in the late 19th century, and when zinc oxide was introduced as a paint pigment in about 1900, the zinc-based paints were advertised as safer alternatives to lead-based paints (and it's about as effective at scattering light as white lead). France banned the use of lead paint for buildings in 1909. In 1921, the League of Nations pushed for lead-free paint.

Many of these laws concerning lead were related to acute lead poisoning, serious lead poisoning from large doses. For paints, the best-known risk was dust from old paint when removing it for re-painting, but the risk to children from eating paint flakes was known (lead paint chips taste sweet, which can encourage children to eat them if they taste one). The long-term effects of acute lead poisoning, and the effects of chronic exposure to lower levels of lead, insufficient to cause the symptoms of acute lead poisoning, were not well known. The known risk of acute lead poisoning was enough for some countries to restrict the use of lead.

With lead paint not being overtly dangerous, as long as stayed on the walls, lead paint continued to be used in many (most!) countries. Lead being cheaper than zinc (on average, about 10% cheaper for much of the 20th century), manufacturers preferred lead over zinc. Rather than switching to the safer but slightly more expensive zinc, the USA saw the formation of the the Lead Industries Association (LIA) in 1928, which advertised the wonderfulness and safety of lead-based paints, and opposed moves by cities and states to regulate the use of lead in paints. The LIA was not the first to do this - for example, in the early 20th century, the National Lead Company (makers of Dutch Boy lead-based paint) advertised that 'Lead Helps to Guard Your Health". Now, the LIA worked for the entire industry. In the 1950s, as the dangers of lead were becoming more widely known, the LIA advocated for voluntary agreements by manufacturers to limit the lead content of paints for indoor use. By then, titanium dioxide had seen use as a paint pigment (since the 1930s), providing even better opacity of the paint (but, like zinc, also being more expensive than lead).

When leaded petrol/gasoline was introduced in the 1920s (in the USA, in 1923), there was debate about its safety. While it was clear that it wouldn't be a likely cause of acute lead poisoning, it would expose more people to more lead than they had been exposed to before. From 1928, downplaying these risks was another job for the LIA, which promoted the idea that the human body was quite efficient at getting rid of small amounts of lead if they were absorbed into the body. There wasn't much in the way of good scientific evidence one way or the other back in the 1920s, but assuming that it was safe in the absence of good evidence, when lead was known to be hazardous, was, by modern scientific and ethical standards, the wrong choice.

The situation regarding evidence changed quickly. By the 1940s, it was clear to medicine and science that low doses of lead were harmful - enough evidence had accumulated in the 1920s and 1930s to be quite convincing. By the 1950s, this was becoming more widely known to the public (thus, more activity by the LIA to convince Americans that lead paint and leaded gasoline were safe). Baltimore was a pioneer in the USA in the control of lead, thanks to their commissioner of health, Huntington Williams. In the 1930s, Williams was responsible to collecting evidence on the safety, or rather the non-safety, of lead, and Baltimore was treating lead as a serious problem by the late 1930s. This lead to Maryland's Toxic Finishes Law of 1949, which banned the use of lead in paints for children's toys and furniture. Unfortunately, this law didn't last for very long - the LIA actively lobbied against it, and it was repealed by the governor in 1950. Industry profits trumped the safety of children.

By the 1960s, it was clear that lead was dangerous, even in small amounts, and at least to science and the U.S. Public Health Service, it was clear that leaded gasoline was a major problem. One landmark scientific paper of the decade was Clair Patterson's "Contaminated and Natural Lead Environments of Man". The LIA surveyed the public to determine their awareness of the risks of lead - the public was well aware of the dangers, but happily for the LIA, only 1% recognised the danger of leaded gasoline - for the public, the dangers of lead meant the dangers of lead-based paints. As more appeared in the press about levels of lead in the atmosphere from leaded gasoline, the LIA simply claimed that these concerns were "entirely without foundation".

Growing public concern in the USA, and the formation of the Environmental Protection Agency in 1970, along with a new willingness for the federal government to pass laws on pollution. In 1972, the EPA moved to reduce lead in gasoline, over the next 5 years. The LIA fought this, contesting the EPA's authority to regulate such things. The courts upheld the EPA's authority, but perhaps in response to the legal battle, they moved slowly and cautiously. The 1970s saw the start towards reducing the use of leaded gasoline, and the banning of lead-based paints, not just in the USA, but also in Canada, Australia, and many other countries.

Leaded gasoline was on the way out, anyway. The US Clean Air Act of 1963 meant that vehicle emissions of nitrogen oxides needed to be reduced, which meant that catalytic converters were on the way in. As the president of General Motors announced to the industry in 1970, this meant that leaded gasoline was on the way out - leaded gasoline was incompatible with the catalytic converter.

So, to return to your original questions, yes, the industry fought regulation of lead, and downplayed the dangers, and opposed regulation in the courts. This was done despite the risks being known, and despite children dying of lead poisoning from lead-based paint. Further, even when lead-based paints were banned in the USA and Canada, manufacturers there continued making lead-based paints for export to countries without such legal protection for the health of their citizens (e.g., India only banned lead-based paints in 2016).

References and further reading:

Roman knowledge of the dangers of lead: http://penelope.uchicago.edu/~grout/encyclopaedia_romana/wine/leadpoisoning.html

Clair C. Patterson (1965), "Contaminated and Natural Lead Environments of Man", Archives of Environmental Health 11:3, 344-360, https://doi.org/10.1080/00039896.1965.10664229

The source for much of this: Markowitz, Gerald, and David Rosner, Lead Wars: The Politics of Science and the Fate of America's Children, University of California Press, 2013.